AMBARI-5118. Update Request resource API doc. (swagle)

ambari-server/docs/api/v1/requests.md

@@ -88,3 +88,26 @@ Get the collection of the requests for the cluster named "c1".
           }
         ]	
     }  	
+
+
+Post on a request resource allows the user to execute Custom commands or custom actions on resources identified by a resource filter.
+Custom Command - A command script defined for Services in the Ambari Services stack and identified by a command name. Example: Restart, Service checks / Decommission slave component.
+Custom Action - A command script defined in the stack under custom_actions and identified by the action definition specified in /custom_action_definitions/system_action_definitions.xml.
+
+    POST http://your.ambari.server/api/v1/clusters/c1/requests
+
+    202 Created
+    {
+       "RequestInfo": {
+          "context": "Restart DataNode",
+          "command": "RESTART"
+       },
+       "Requests/resource_filters": [
+          {
+             "service_name": "HDFS",
+             "component_name": "NAMENODE",
+             "hosts": "host1,host2,host3"
+          }
+       ]
+    }
+