Allow disabling security groups

For some use cases it might be needed to disable security groups.
For example best DPDK performance can be achieved only with disabled
security groups.

Change-Id: I067fa230c0cc5f8042bc405249f99e09250893ec
diff --git a/README.rst b/README.rst
index e8e633f..d3a64ae 100644
--- a/README.rst
+++ b/README.rst
@@ -707,6 +707,20 @@
           map_file: '/etc/pycadf/neutron_api_audit_map.conf'
       ....
 
+Neutron with security groups disabled
+
+.. code-block:: yaml
+
+    neutron:
+      server:
+        security_groups_enabled: False
+      ....
+      compute:
+        security_groups_enabled: False
+      ....
+      gateway:
+        security_groups_enabled: False
+
 
 Neutron Client
 --------------