Add docs, changelog file

changelog/unreleased/issue-2135

@@ -0,0 +1,10 @@
+Bugfix: Return error when no bytes could be read from stdin
+
+We assume that users reading backup data from stdin want to know when no data
+could be read, so now restic returns an error when `backup --stdin` is called
+but no bytes could be read. Usually, this means that an earlier command in a
+pipe has failed. The documentation was amended and now recommends setting the
+`pipefail` option (`set -o pipefail`).
+
+https://github.com/restic/restic/pull/2135
+https://github.com/restic/restic/pull/2139

doc/040_backup.rst

@@ -286,6 +286,7 @@ this mode of operation, just supply the option ``--stdin`` to the
 
 .. code-block:: console
 
+    $ set -o pipefail
     $ mysqldump [...] | restic -r /srv/restic-repo backup --stdin
 
 This creates a new snapshot of the output of ``mysqldump``. You can then
@@ -299,6 +300,13 @@ specified with ``--stdin-filename``, e.g. like this:
 
     $ mysqldump [...] | restic -r /srv/restic-repo backup --stdin --stdin-filename production.sql
 
+The option ``pipefail`` is highly recommended so that a non-zero exit code from
+one of the programs in the pipe (e.g. ``mysqldump`` here) makes the whole chain
+return a non-zero exit code. Refer to the `Use the Unofficial Bash Strict Mode
+<http://redsymbol.net/articles/unofficial-bash-strict-mode/>`__ for more
+details on this.
+
+
 Tags for backup
 ***************