Allow specify flat networks

Some customers want to be able to specify the exact list of flat
networks or to disable flat networks due to security reasons

Change-Id: Ic61f266349eb99fa6d96eeee382a7719fb7fe8be
Related-Prod: PROD-21077
diff --git a/README.rst b/README.rst
index a5f8e8a..d51c7b5 100644
--- a/README.rst
+++ b/README.rst
@@ -695,14 +695,22 @@
           ...
           # also need to configure corresponding bridge_mappings on
           # compute and gateway nodes
+          flat_networks_default: '*' # '*' to allow arbitrary names or '' to disable
           physnets: # only listed physnets will be configured (overrides physnet1/2/3)
             external:
               mtu: 1500
+              types:
+                - flat # possible values - 'flat' or 'vlan'
             sriov_net:
               mtu: 9000 # Optional, defaults to 1500
               vlan_range: '100:200' # Optional
+              types:
+                - vlan
             ext_net2:
               mtu: 1500
+              types:
+                - flat
+                - vlan
           mechanism:
             ovs:
               driver: openvswitch