Policy.json should be defined by user

User can override and add values to policy.json by creating flat
key-value structure under cinder:controller:policy.

Change-Id: I1d58c632442cd1ffb19f2020ab9e5e63bea975a9
diff --git a/README.rst b/README.rst
index 3296d86..4cdd914 100644
--- a/README.rst
+++ b/README.rst
@@ -168,6 +168,18 @@
         wipe_method: shred
         ...
 
+Configuration of policy.json file
+
+.. code-block:: yaml
+
+    cinder:
+      controller:
+        ....
+        policy:
+          'volume:delete': 'rule:admin_or_owner'
+          # Add key without value to remove line from policy.json
+          'volume:extend':
+
 
 Default Cinder setup with iSCSI target