feature request: instance bookmarks

Hello,

I lurk into some thematic instances very often, without being necessarily subscribed to all communities there, but this is a hard task to do as lemmy is right now: I need to know the instance as first, then I need to open it in another window... and finally, if I decide I want to subscribe to a community there I need to comeback to my own instance and look for the community to hit the join button.

I think it would be a nice addition to be able to bookmark instances and then browse their local feed by clicking there... a super extra bonus would be being able to subscribe to extra-communities from there.