add beta link

Author: terryzfeng

index.html

@@ -156,6 +156,10 @@
                         <a href="https://chuck.stanford.edu/community" class="btn btn-link" target="_blank">Community</a> 
                     </ul>
                 </div>
+                <!-- BETA -->
+                <div style="width: 100%; text-align: right; padding-right: 8px;">
+                    <a href="https://ccrma.stanford.edu/~tzfeng/webchuck-ide"  target="_blank" style="color: #2563eb"><b>Try the new WebChucK IDE!</b></a>
+                </div>
             </section>
         </header>