Add a link to the feed repo's new location

[seagreen]

Hackage currently has the repo for feed set to https://github.com/bergmark/feed. Add a README with a note directing users to that new location. If you'd like me to make a PR for this I'll be happy to.

[tippenein]

I think the right way to do this is with a change of ownership, s/t bergmark becomes the new owner (right now the main repo is a fork, which is strange)