Add posibilitty to configure neutron server default_availability_zones

Closes-Bug: PROD-35166
Change-Id: I6dab42ab6ff75f612ecfbd8638f0354ae8b82f68
diff --git a/README.rst b/README.rst
index 1c3be16..25eb136 100644
--- a/README.rst
+++ b/README.rst
@@ -1796,6 +1796,20 @@
       ....
 
 
+Defining default_availability_zones:
+------------------------------------
+
+Control node:
+
+.. code-block:: yaml
+
+    neutron:
+      ....
+      server:
+        default_availability_zones: 'custom_az1, custom_az2'
+      ....
+
+
 Set nova_metadata_protocol for Neutron
 ---------------------------------------