Explicit format in command.

spec/README.md

@@ -176,7 +176,8 @@ respond to an external event (e.g.  an incoming HTTP request).
 
 #### List routes
 
-Returns JSON data about the current routes.
+Returns JSON with all data about the current routes. Be aware that the command
+field must be a json scaped string.
 
 * **URL**: `/routes`
 * **Method**: `GET`