Add BGP VPN Interconnection Service

The service aims at supporting inter-connection between L3VPNs
and Neutron resources, i.e. Networks, Routers and Ports.
The framework is generic to also support E-VPN [RFC7432],
which inherits the same protocol architecture as BGP/MPLS IP VPNs.

Related-Prod: PROD-17612
Change-Id: I236016669160f5bc6b52d5563b6471be820ec271
diff --git a/README.rst b/README.rst
index afcc972..0209dd6 100644
--- a/README.rst
+++ b/README.rst
@@ -747,6 +747,28 @@
       gateway:
         vlan_aware_vms: true
 
+Neutron with BGP VPN
+---------------------------
+
+.. code-block:: yaml
+
+    neutron:
+      server:
+        version: pike
+        bgp_vpn:
+          enabled: false
+          driver: bagpipe # Options: bagpipe/opencontrail/opendaylight
+      ....
+      compute:
+        version: pike
+        bgp_vpn:
+          enabled: false
+          driver: bagpipe # Options: bagpipe/opencontrail/opendaylight
+        backend:
+          extension:
+            bagpipe_bgpvpn:
+              enabled: True
+
 Neutron with DHCP agent on compute node
 ---------------------------------------