[Feature Request] Web Feed

Hello,

I would like to provide a web feed (`rss.xml` and / or `atom.xml`) with an item per recipe

I would expect that `cook build web` generates those files

Start at the `cook build web` entry point and inspect how the web output is generated. Add `rss.xml` and/or `atom.xml` alongside that output, with one item per recipe, then verify that running `cook build web` creates the feed file(s).

Written by the indexing model from the issue text.