Implement rewind, add a key for it, and suggest keys in general

index.html

@@ -56,6 +56,7 @@
             <h1 class="-top"></h1>
             <div class="-middle"></div>
             <p class="-bottom"></p>
+            <p class="-keyhint"></p>
         </div>
         <div class="message"></div>
         <div class="chips">