Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/commands.json

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   {
     "namespace": "commands",
+    "description": "Use the commands API to add keyboard shortcuts that trigger actions in your extension, for example, an action to open the browser action or send a command to the extension.",
     "types": [
       {
         "id": "Command",
         "type": "object",
         "properties": {
           "name":        {
             "type": "string",
             "optional": true,
             "description": "The name of the Extension Command"
           },
@@ skipping 42 matching lines @@
                 }
               }
             ],
             "description": "Called to return the registered commands."
           }
         ]
       }
     ]
   }
 ]