Add jqplay link to the site

docs/templates/shared/_header.liquid

@@ -17,6 +17,7 @@
           {% endfor %}
           <li><a href="https://github.com/stedolan/jq/issues">Issues</a></li>
           <li><a href="https://github.com/stedolan/jq">Source</a></li>
+          <li><a href="http://jqplay.org">Try online</a></li>
         </ul>
       </div>
     </div>