add gallery page, fill with a few screenshots to start

docs/javascript.html

@@ -58,6 +58,9 @@
             <li class="">
               <a href="./customize.html">Customize</a>
             </li>
+            <li class="">
+              <a href="./gallery.html">Gallery</a>
+            </li>
           </ul>
         </div>
       </div>