title: Add icon to submit button in twitter bootstrap 2
body: <p>I want to use the twitter bootstrap icons on my form input submit buttons. </p>
  
  <p>The examples on <a href="http://twitter.github.com/bootstrap/base-css.html#icons" rel="noreferrer">http://twitter.github.com/bootstrap/base-css.html#icons</a> mainly show styled hyperlinks. </p>
  
  <p>The closest I've come is getting the icon displayed next to the button, but not inside.</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;div class="input-prepend"&gt;
     &lt;span class="add-on"&gt;&lt;i class="icon-user icon-white"&gt;&lt;/i&gt;&lt;/span&gt;
     &lt;input type="submit" class="btn-primary" value="Login" &gt;
  &lt;/div&gt;
  </code></pre>