Here's a small example from a project of mine...
...and the code is something like this:
HTML
<div class="form-group has-feedback">
<input type="text" class="form-control" placeholder="Enter location or place">
<span class="fa fa-map-marker form-control-feedback" aria-hidden="true"></span>
</div>
This is almost letter-to-letter copy/paste of Bootstrap examples of form feedback with optional icons, the major difference is that all the 'glyphicon' classes are replaced by 'fa' classes for Font Awesome icons.
Enjoy!
-i