Add RSS support

[Denubis]

Looking at the blog infrastructure for evidence.dev (It'd be amazing if you could point to it being generated by evidence.dev), there aren't any rss feeds referenced in the page metadata. Considering your audience, I suspect not everyone is particularly inclined to give out an email.

[mcrascal]

@Denubis That's a great idea. Our website is an evidence project (except the docs, but we'll migrate them eventually).

I am going to update this to track adding RSS support to evidence in general, rather than just our blog.