Also mention the "no justified navbars" limitation in the Nav docs

Refs #14598
[skip sauce]

docs/_includes/components/navs.html

@@ -57,6 +57,7 @@
 
   <h2 id="nav-justified">Justified</h2>
   <p>Easily make tabs or pills equal widths of their parent at screens wider than 768px with <code>.nav-justified</code>. On smaller screens, the nav links are stacked.</p>
+  <p><strong class="text-danger">Justified navbar nav links are currently not supported.</strong></p>
   <div class="bs-callout bs-callout-warning">
     <h4>Safari and responsive justified navs</h4>
     <p>As of v7.1, Safari exhibits a bug in which resizing your browser horizontally causes rendering errors in the justified nav that are cleared upon refreshing. This bug is also shown in the <a href="../examples/justified-nav/">justified nav example</a>.</p>