Parametrized multi_tenancy to enable/disable authentication to Contrail API

Change-Id: I30ef75171a64e9212c4fb296298617316007d2a9
diff --git a/README.rst b/README.rst
index f414d29..576d2ae 100644
--- a/README.rst
+++ b/README.rst
@@ -602,6 +602,20 @@
         engine: kubernetes
       ...
 
+Disable Contrail API authentication
+-----------------------------------
+
+Contrail version must >=3.0. It is useful especially for Keystone v3.
+
+.. code-block:: yaml
+
+    opencontrail:
+      ...
+      config:
+        multi_tenancy: false
+      ...
+
+
 Usage
 =====