Feature proposal: RSS/atom feeds get an icon by default

Hello! I feel a little silly starting a whole thread for such a tiny proposal, but I would like to open this one-line PR to add an <icon> element to the built-in Atom feed template:

This uses your configured config.extra.favicon path, if you have one, and omits the icon otherwise.

Any objections to my opening this PR?

Since it comes from extra, I don’t think it makes sense to have that builtin. It’s easy for a user to update the template if necessary

OK! But to be clear, this doesn’t have to be in extra. Like the description field, it’s useful for feeds and other metadata but not strictly required. If icon were a top-level config option, templates could use it in HTML headers as well.