add user guide link

css/common/common.less

@@ -217,6 +217,15 @@ body, html {
     color: #333
 }
 
+.userguide {
+    position: absolute;
+    color: #FFF;
+    right: 2px;
+    top: 24px;
+    color: #333;
+}
+
+
 // modal
 
 .modal {

css/common/ico.less

@@ -63,6 +63,10 @@
     .i-ico('\e01e');
 }
 
+.i-help {
+    .i-ico('\e016');
+}
+
 // 编辑器按钮组
 .i-new {
     .i-ico('\e019');

index.html

@@ -78,7 +78,9 @@
                 </ul>
             </div>
         </div>
+
         <a class="ico i-github forkme" href="https://github.com/ecomfe/fonteditor" target="_blank">Fork me on Github</a>
+        <a class="ico i-help userguide" href="./doc/index.html" target="_blank">帮助</a>
     </section>
 
     <section class="sidebar">