Update the demo URL

Author: ShreckYe

site/index.html

@@ -21,11 +21,11 @@
     <ul>
         <li><a href="api-documentation/index.html">API documentation</a></li>
         <li>
-            <a href="https://huanshankeji.github.io/compose-multiplatform-html-unified/">
+            <a href="https://huanshankeji.github.io/compose-multiplatform-html-unified/demo/index.html">
                 Compose Multiplatform HTML Unified side-by-side demo
             </a>
         </li>
     </ul>
 </body>
 
-</html>
+</html>