Clarify the use of .has-feedback

docs/css.html

@@ -1976,7 +1976,7 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
 {% endhighlight %}
 
   <h3>With optional icons</h3>
-  <p>You can also add optional feedback icons with the addition of an extra class and the right icon.</p>
+  <p>You can also add optional feedback icons with the addition of <code>.has-feedback</code> and the right icon.</p>
   <div class="bs-callout bs-callout-warning">
     <h4>Icons and input groups</h4>
     <p>When using the feedback icons, be aware that manual positioning may be required for <a href="../components#input-groups">input groups</a> with an add-on on the right. Adjust the <code>right: 0;</code> to an appropriate pixel value depending on the width of your addon.</p>