Keystone v3 support for opencontrail

Change-Id: I230438c62aaf9a95f8760f0daeed242906ecd132
diff --git a/README.rst b/README.rst
index 00f152f..a539898 100644
--- a/README.rst
+++ b/README.rst
@@ -7,6 +7,33 @@
 Sample pillars
 ==============
 
+Keystone v3
+-------------
+
+To enable support for keystone v3 in opencontrail, there must be defined version for config and web role.
+
+.. code-block:: yaml
+
+    opencontrail:
+      config:
+        version: 2.2
+        enabled: true
+        ...
+        identity:
+          engine: keystone
+          version: '3'
+        ...
+
+    opencontrail:
+      web:
+        version: 2.2
+        enabled: true
+        ...
+        identity:
+          engine: keystone
+          version: '3'
+        ...
+
 Usage
 =====