Add ngx_http_limit_conn_module functionality

Add posibility to limit the number of connections per the defined key

Change-Id: Ic05f9c4a4904ea4293889bc3d88d0122525df1b0
Related-Prod: PROD-24400
diff --git a/README.rst b/README.rst
index 0e04cf8..6e28916 100644
--- a/README.rst
+++ b/README.rst
@@ -415,6 +415,42 @@
                   enabled: true
 
 
+Use `ngx_http_limit_conn_module` module that is used to set the shared memory
+zone and the maximum allowed number of connections for a given key value.
+The `limit_conn_module` might be configured globally or applied to specific
+nginx site.
+
+.. code-block:: yaml
+
+    nginx:
+      server:
+        limit_conn_module:
+          limit_conn_zone:
+            global_limit_conn_zone:
+              key: 'binary_remote_addr'
+              size: 10m
+          limit_conn_status: 503
+          limit_conn:
+             global_limit_conn_zone:
+               connection: 50
+               enabled: true
+
+
+To apply connection limiting to particular site only `limit_conn` should be
+applied on site level, for example:
+
+.. code-block:: yaml
+
+    nginx:
+      server:
+        site:
+          nginx_proxy_openstack_web:
+            limit_conn_module:
+              limit_conn:
+                global_limit_conn_zone:
+                  connections: 25
+                  enabled: true
+
 Gitlab server with user for basic auth:
 
 .. code-block:: yaml