Support feed autodiscovery

[telekid]

I'd love to be able to add a feed by pasting in a page URL rather than a feed URL.

More context here:
https://blog.whatwg.org/feed-autodiscovery
https://www.rssboard.org/rss-autodiscovery

[hfellerhoff]

Totally agree! I'll make sure to bump this up in my priority list.