One should be able to set path_mtu value for neutron

Customer-Found
Change-Id: Ie100e957aeeba3a8e1747513b0793aeee5b7cd76
diff --git a/README.rst b/README.rst
index 416f93b..502d5c5 100644
--- a/README.rst
+++ b/README.rst
@@ -157,6 +157,7 @@
     neutron:
       server:
         version: mitaka
+        path_mtu: 1500
         bind:
           address: 172.20.0.1
           port: 9696