Add support of flow_cache_timeout parameter for contrail-vrouter-agent

Change-Id: I25655d18d447f36261443bba117b352bb82a1703
Related-PROD: PROD-30104
diff --git a/README.rst b/README.rst
index bf4fe01..829e827 100644
--- a/README.rst
+++ b/README.rst
@@ -1533,6 +1533,22 @@
         nodemgr: 10
       ....
 
+Define aging time for flow-records in seconds
+---------------------------------------------
+
+Flows are aged out based on inactivity for a specific period of time. By default,
+the timeout value is 180 seconds. This can be modified by configuring flow_cache_timeout for
+contrail-vrouter-agent service:
+
+.. code-block:: yaml
+
+    opencontrail:
+      ....
+      compute
+        ....
+        flow_cache_timeout: 180
+        ....
+
 Usage
 =====