add a quick little example of icons in buttons

docs/base-css.html

@@ -1323,6 +1323,9 @@ Form states
       <p>Essentially, anywhere you can put an <code>&lt;i&gt;</code> tag, you can put an icon.</p>
     </div>
   </div>
+
+  <h3>Examples</h3>
+  <p><a class="btn" href="#"><i class="check"></i> Button</a></p>
 </section>