Ability to set number of backupninja backups to keep

Change-Id: I27c4c6995a3d40c6c6210c258f53773fc3d6fdaf
diff --git a/README.rst b/README.rst
index 9392502..a05787b 100644
--- a/README.rst
+++ b/README.rst
@@ -115,6 +115,21 @@
 ..note:: Parameter ``auto_backup_disabled`` is optional. It disables automatic
   backup when set to true. It's set to ``false``by default when not defined.
 
+Backup client with defined number of backups to keep:
+
+..code-block:: yaml
+
+    backupninja:
+      client:
+        enabled: true
+          engine: rsync
+          host: 10.10.10.208
+          user: backupninja
+          keep: 4
+
+  ..note:: The ``keep`` parameter defines number of backups to keep. If not
+    defined it's set to ``7`` by default.
+
 Backup server rsync/rdiff
 
 .. code-block:: yaml