docs: added the "delete" subsection in the configuration.md file

Signed-off-by: Miquel Sabaté <msabate@suse.com>

docs/configuration.md

@@ -112,6 +112,8 @@ information about each option that appears later in this page.
         region: fr
         container: containername
         rootdirectory: /swift/object/name/prefix
+      delete:
+        enabled: false
       redirect:
         disable: false
       cache:
@@ -330,6 +332,8 @@ Permitted values are `error`, `warn`, `info` and `debug`. The default is
         region: fr
         container: containername
         rootdirectory: /swift/object/name/prefix
+      delete:
+        enabled: false
       cache:
         blobdescriptor: inmemory
       maintenance:
@@ -348,6 +352,15 @@ If you are deploying a registry on Windows, be aware that a Windows volume mount
 
     mkdir /XXX protocol error and your registry will not function properly.
 
+### delete
+
+Use the `delete` subsection to enable the deletion of image blobs and manifests
+by digest. It defaults to false, but it can be enabled by writing the following
+on the configuration file:
+
+    delete:
+      enabled: true
+
 ### cache
 
 Use the `cache` subsection to enable caching of data accessed in the storage