Just Copy and Paste the lines below into your HTML:

<div id="showdown-widget-1"><a href="http://developer.ubuntu.com/"><img src="http://bholtsclaw.github.com/img/nojs.png" style="border: 0;"></a></div>
<script src="http://bholtsclaw.github.com/showdown/1/loader.js" type="text/javascript"></script>

NOTE You can place the script tag anywhere you like, putting it just before the closing body tag is considered best practice, but not required. The Div should be where you would like the widget for the countdown to be rendered. Also make sure to check back here now and then as I'll be adding more themes to choose from and maybe even add a RSS feed to let you know when I add new widgets!