docs: update rclone about docs

Create a full loop of documentation for rclone about, backends overview
and individual backend pages.

Discussion:
https://github.com/rclone/rclone/pull/4774 relates

Previously pull was requested, in part, under ref
https://github.com/rclone/rclone/pull/4801

Notes:
Introduce a tentative draft see-link format the end of sections to try
rather than lots of in-para links.

Update about.go incl link to list of backends not supporting about.

In list of backends not supporting about, include link to about command
reference.

I appreciate there may be decisions to make going forward about whether
command links should be code formatted, and using proper pretty url
links, but I have fudged that for now.

Update backend pages that do not support about with wording used
previously for ftp - it is in passive voice but I can live with it. (my
own wording and fault). The note is applied to a limitations section. If
one does not already exist it is created (even if there are other
limitations with their own sections)

docs/content/amazonclouddrive.md

@@ -307,3 +307,12 @@ because of file size, so it will retry the operation, as any other
 failure. To avoid this problem, use `--max-size 50000M` option to limit
 the maximum size of uploaded files. Note that `--max-size` does not split
 files into segments, it only ignores files over this size.
+
+`rclone about` is not supported by the Amazon Drive backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/azureblob.md

@@ -327,12 +327,19 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,BackSlash,Del,Ctl,RightPeriod,InvalidUtf8
 
 {{< rem autogenerated options stop >}}
-
 ### Limitations ###
 
 MD5 sums are only uploaded with chunked files if the source has an MD5
 sum.  This will always be the case for a local to azure copy.
 
+`rclone about` is not supported by the Microsoft Azure Blob storage backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+
 ### Azure Storage Emulator Support ###
 You can test rclone with storage emulator locally, to do this make sure azure storage emulator
 installed locally and set up a new remote with `rclone config` follow instructions described in

docs/content/b2.md

@@ -513,4 +513,14 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,BackSlash,Del,Ctl,InvalidUtf8,Dot
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the B2 backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+
 

docs/content/box.md

@@ -408,3 +408,12 @@ and from an identical looking unicode equivalent `＼` (U+FF3C Fullwidth
 Reverse Solidus).
 
 Box only supports filenames up to 255 characters in length.
+
+`rclone about` is not supported by the Box backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/fichier.md

@@ -151,3 +151,13 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,LtGt,DoubleQuote,SingleQuote,BackQuote,Dollar,BackSlash,Del,Ctl,LeftSpace,RightSpace,InvalidUtf8,Dot
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the 1Fichier backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/ftp.md

@@ -229,7 +229,6 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 
 ### Limitations ###
 
-
 Modified times are not supported. Times you see on the FTP server
 through rclone are time of upload.
 
@@ -239,7 +238,10 @@ file sizes.
 `rclone about` is not supported by the FTP backend. Backends without
 this capability cannot determine free space for an rclone mount or
 use policy `mfs` (most free space) as a member of an rclone union
-remote. [More](https://rclone.org/overview/#optional-features)
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
 
 The implementation of : `--dump headers`,
 `--dump bodies`, `--dump auth` for debugging isn't the same as

docs/content/googlecloudstorage.md

@@ -509,3 +509,13 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,CrLf,InvalidUtf8,Dot
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the Google Cloud Storage backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/googlephotos.md

@@ -234,6 +234,14 @@ are stored in full resolution at "original quality" and **will** count
 towards your storage quota in your Google Account.  The API does
 **not** offer a way to upload in "high quality" mode..
 
+`rclone about` is not supported by the Google Photos backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+
 ### Downloading Images
 
 When Images are downloaded this strips EXIF location (according to the

docs/content/http.md

@@ -186,3 +186,13 @@ If you set this option, rclone will not do the HEAD request.  This will mean
 - Default:     false
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the HTTP backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/opendrive.md

@@ -163,3 +163,12 @@ platforms they are common.  Rclone will map these names to and from an
 identical looking unicode equivalent.  For example if a file has a `?`
 in it will be mapped to `？` instead.
 
+`rclone about` is not supported by the OpenDrive backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+
+

docs/content/overview.md

@@ -439,6 +439,8 @@ Backends without about capability cannot determine free space for an
 rclone mount, or use policy `mfs` (most free space) as a member of an
 rclone union remote.
 
+See [rclone about command](https://rclone.org/commands/rclone_about/)
+
 ### EmptyDir ###
 
 The remote supports empty directories. See [Limitations](/bugs/#limitations)

docs/content/qingstor.md

@@ -283,3 +283,13 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,Ctl,InvalidUtf8
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the qingstor backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/s3.md

@@ -2430,8 +2430,19 @@ Name                 Type
 cos                  s3
 ```
 
-### Netease NOS  ###
+### Netease NOS
 
 For Netease NOS configure as per the configurator `rclone config`
 setting the provider `Netease`.  This will automatically set
 `force_path_style = false` which is necessary for it to run properly.
+
+### Limitations
+
+`rclone about` is not supported by the S3 backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/sharefile.md

@@ -232,3 +232,13 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,LtGt,DoubleQuote,Colon,Question,Asterisk,Pipe,BackSlash,Ctl,LeftSpace,LeftPeriod,RightSpace,RightPeriod,InvalidUtf8,Dot
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the Citrix ShareFile backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/sugarsync.md

@@ -249,3 +249,13 @@ See: the [encoding section in the overview](/overview/#encoding) for more info.
 - Default:     Slash,Ctl,InvalidUtf8,Dot
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the SugarSync backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+

docs/content/tardigrade.md

@@ -300,3 +300,13 @@ Encryption Passphrase. To access existing objects enter passphrase used for uplo
 - Default:     ""
 
 {{< rem autogenerated options stop >}}
+### Limitations
+
+`rclone about` is not supported by the rclone Tardigrade backend. Backends without
+this capability cannot determine free space for an rclone mount or
+use policy `mfs` (most free space) as a member of an rclone union
+remote.
+
+See [List of backends that do not support rclone about](https://rclone.org/overview/#optional-features)
+See [rclone about](https://rclone.org/commands/rclone_about/)
+