mention responsive css in navbar responsive section

docs/components.html

@@ -1073,7 +1073,7 @@
 </div>
 </pre>
       <div class="alert alert-info">
-        <strong>Heads up!</strong> The responsive navbar requires the <a href="./javascript.html#collapse">collapse plugin</a>.
+        <strong>Heads up!</strong> The responsive navbar requires the <a href="./javascript.html#collapse">collapse plugin</a> and <a href="./scaffolding.html#responsive">responsive Bootstrap CSS file</a>.
       </div>
 
     </div><!-- /.span -->

docs/templates/pages/components.mustache

@@ -996,7 +996,7 @@
 </div>
 </pre>
       <div class="alert alert-info">
-        <strong>{{_i}}Heads up!{{/i}}</strong> The responsive navbar requires the <a href="./javascript.html#collapse">collapse plugin</a>.
+        <strong>{{_i}}Heads up!{{/i}}</strong> The responsive navbar requires the <a href="./javascript.html#collapse">collapse plugin</a> and <a href="./scaffolding.html#responsive">responsive Bootstrap CSS file</a>.
       </div>
 
     </div><!-- /.span -->