append new demo

Author: dabeng

demo/index.html

@@ -137,6 +137,7 @@
     <li><a href="toggle-sibs-resp.html" target="_blank">toggle sibling nodes respectively</a></li>
     <li><a href="ul-datasource.html" target="_blank">ul datasource</a></li>
     <li><a href="vertical-level.html" target="_blank">hybrid(horizontal + vertical) chart</a></li>
+    <li><a href="responsive-design.html" target="_blank">responsive design</a></li>
     <li><a href="custom-template.html" target="_blank">template for internal structure of node</a></li>
   </ol>
   </section>