docs: Use https link for 'how to read documentation' information

Author: coliff

src/default_theme/index._

@@ -88,7 +88,7 @@
             </ul>
           </div>
           <div class='mt1 h6 quiet'>
-            <a href='http://documentation.js.org/reading-documentation.html'>Need help reading this?</a>
+            <a href='https://documentation.js.org/reading-documentation.html'>Need help reading this?</a>
           </div>
         </div>
       </div>