I second siscla's comment. Why go to the trouble of posting this without explaining how to use it? And do you have a sample rss_footer.html file anywhere? Where do you place this file? How does jekyll know to put it in a feed directory? Help us here, Paul.
This file works simply like all other Jekyll files. Drop it in the main directory, name it something like atom.xml and it will be generated with your site. Then you can link to it if you'd like just how you would any other page.