Create listing of game engines with links to packaged app instructions.

chrome/common/extensions/docs/templates/json/chrome_sidenav.json

 [
   {
     "title": "Devtools",
     "items": [
       {
         "title": "Learn Basics",
         "items": [
           {
             "title": "Overview",
             "href": "/devtools/index"
@@ skipping 412 matching lines @@
                 "title": "About MVC Architecture",
                 "href": "/apps/app_frameworks"
               },
               {
                 "title": "Build Apps with AngularJS",
                 "href": "/apps/angular_framework"
               },
               {
                 "title": "Build Apps with SenchaJS",
                 "href": "/apps/sencha_framework"
+              },
+              {
+                "title": "Game Engines",
+                "href": "/apps/game_engines"
               }
             ]
           },
           {
             "title": "Distribute Apps",
             "href": "/apps/publish_app",
             "items": [
               {
                 "title": "Publish Your App",
                 "href": "/apps/publish_app"
@@ skipping 554 matching lines @@
                 "title": "Articles",
                 "href": "/webstore/articles"
               }
             ]
           }
         ]
       }
     ]
   }
 ]