New getting started tutorial for sencha media player app.

chrome/common/extensions/docs/templates/private/apps_sidenav.html

 <div class="g-unit g-first" id="gc-sidebar">
   <ul>
     <li><span>Getting Started</span>
       <ul>
         <li><a href="about_apps.html">What Are Packaged Apps?</a></li>
         <li><a href="app_architecture.html">Understand the Architecture</a></li>
         <li><a href="first_app.html">Create Your First App</a></li>
       </ul>
     </li>
     <li><span>Developing</span>
@@ skipping 13 matching lines @@
               <li><a href="app_csp.html">Comply with CSP</a></li>
             </ul>
           </li>
           <li><span>Advanced Technologies</span>
             <ul toggleable>
               <li><a href="app_network.html">Network Communications</a></li>
               <li><a href="app_hardware.html">Access Hardware Devices</a></li>
               <li><a href="app_intents.html">Connect Apps with Web Intents</a></li>
             </ul>
           </li>
-          <li><a href="app_frameworks.html">MVC Architecture</a></li>
+          <li><span><a href="app_frameworks.html">MVC Architecture</a></span>
+            <ul toggleable>
+              <li><a href="sencha_framework.html">Build Apps with Sencha Ext JS</a></li>
+            </ul>
+          </li>
         </ul>
       </li>
       <li><span>Deploying</span>
         <ul>
           <li><a href="publish_app.html">Publish</a></li>
         </ul>
       </li>
       <li><span>Reference</span>
         <ul>
           <li><a href="manifest.html">Manifest Files</a></li>
           <li><a href="api_index.html">Chrome JavaScript APIs</a></li>
           <li><a href="api_other.html">Supported Libraries</a></li>
           <li><a href="app_deprecated.html">Disabled Web Features</a></li>
         </ul>
       </li>
       <li><span><a href="samples.html">Samples</a></span></li>
       <li><span><a href="app_known_issues.html">Known Issues</a></span></li>
   </ul>
 </div>