Mention support for Atom feeds in readme

[yagarea]

From readme of this repo I understand that only RSS feeds are supported. Atom feed is newer and more versatile format for checking updates on website: validator.w3.org/feed/docs/atom.html.

Basically all of RSS readers support atom these days so its a missed opportunity to not include them.

[yagarea]

From checking smallweb.txt file atom feeds seem o be supported. So maybe just the README.md is misguiding.

[vprelovac]

We support all kind of feeds, please feel free to edit readme or suggest edit to make it clearer.