doc: Add rclone backend to the manual

doc/030_preparing_a_new_repo.rst

@@ -375,12 +375,59 @@ bucket ``foo`` at the root path:
     [...]
 
 The number of concurrent connections to the GCS service can be set with the
-`-o gs.connections=10`. By default, at most five parallel connections are
+``-o gs.connections=10``. By default, at most five parallel connections are
 established.
 
 .. _service account: https://cloud.google.com/storage/docs/authentication#service_accounts
 .. _create a service account key: https://cloud.google.com/storage/docs/authentication#generating-a-private-key
 
+Other Services via rclone
+*************************
+
+The program `rclone`_ can be used to access many other different services and
+store data there. First, you need to install and `configure`_ rclone. When you
+configure a remote named ``foo``, you can then call restic as follows to
+initiate a new repository in the path ``bar`` in the repo:
+
+.. code-block:: console
+
+    $ restic -r rclone:foo:bar init
+
+As a more concrete example, suppose you have configured a remote named
+``b2prod`` for Backblaze B2 with rclone, with a bucket called ``yggdrasil``.
+You can then use rclone to list files in the bucket like this:
+
+.. code-block:: console
+
+    $ rclone ls b2prod:yggdrasil
+
+In order to create a new repository in the root directory of the bucket, call
+restic like this:
+
+.. code-block:: console
+
+    $ restic -r rclone:b2prod:yggdrasil
+
+If you want to use the path ``foo/bar/baz`` in the bucket instead, pass this to
+restic:
+
+.. code-block:: console
+
+    $ restic -r rclone:b2prod:yggdrasil/foo/bar/baz
+
+Listing the files of an empty repository directly with rclone should return a
+listing similar to the following:
+
+
+.. code-block:: console
+
+    $ rclone ls b2prod:yggdrasil/foo/bar/baz
+        155 bar/baz/config
+        448 bar/baz/keys/4bf9c78049de689d73a56ed0546f83b8416795295cda12ec7fb9465af3900b44
+
+.. _rclone: https://rclone.org/
+.. _configure: https://rclone.org/docs/
+
 Password prompt on Windows
 **************************