Add faq page.

docs/index.html

@@ -42,6 +42,9 @@
                 <li>
                     <a href="examples.html" data-zh="例子">Examples</a>
                 </li>
+                <li>
+                    <a href="faq.html" data-zh="常见问题">FAQ</a>
+                </li>
                 <!-- Localization -->
                 <li id="locale" class="">
                     <a href="#" class="dropdown-toggle" data-toggle="dropdown">