Update api.rst

Author: dskoda1

docs/api.rst

@@ -3,7 +3,19 @@
 XML-RPC API Documentation
 =========================
 
-To use the XML-RPC interface, connect to supervisor's HTTP port
+
+
+
+
+To use the XML-RPC interface, first make sure it has been configured 
+properly by specifying the rpcinterface_factory in your conf file:
+
+.. code-block:: ini
+    
+    [rpcinterface:supervisor]  
+    supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface
+
+Then you can connect to supervisor's HTTP port
 with any XML-RPC client library and run commands against it.  An
 example of doing this using Python's ``xmlrpclib`` client library
 is as follows.