Add feature: is-expanded to navbar-item (#1320)

docs/documentation/components/navbar.html

@@ -736,6 +736,9 @@ document.addEventListener('DOMContentLoaded', function () {
           <code>navbar-dropdown</code>
         </li>
       </ul>
+      <p>
+        You can add the modifier class <code>is-expanded</code> to turn it into a full-width element.
+      </p>
     </div>
 
     {% include anchor.html name="Transparent navbar" %}