add menu entry for the progressbar displayValue demo

Author: nyordanov

demos/progressbar/index.html

@@ -13,6 +13,7 @@ <h4>Examples</h4>
 		<li class="demo-config-on"><a href="default.html">Default functionality</a></li>
 		<li><a href="animated.html">Animated</a></li>
 		<li><a href="resize.html">Resizable progressbar</a></li>
+		<li><a href="displayvalue.html">Display value</a></li>
 	</ul>
 </div>