Adding a RSS feed auto-discovery code to your site is essentially a usability feature. It allows browsers capable of RSS auto discovery such as IE7, Firefox and Safari to display a nice RSS icon RSS.
How to do that?
add below code to your rss feed after <?xml version="1.0" ?>
<link rel="alternate" type="application/rss+xml" title="Top new 20 posts rated" href="http://www.xxxx.com/rss" />
for ATOM feed
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:xxxx="http://www.xxxx.com/">
where http://www.xxxx.com/rss is the feed url
Let me know if you need more info.