Update source repo url. Notify EOL of the website.

Hi Alex. Firstly I'd like to thank you for the great package you wrote. It is integrated in Emacs very nicely and I use it all the time. Since the official repo got moved to codeberg, I've contributed a couple commits and eventually got maintainer hat for the package.

Currently I'm working on the next release: https://codeberg.org/guix/emacs-guix/pulls/14

I'd like to ask you to archive gitlab repos and update the website to point to the new location, to avoid confusion to the users that stumble upon inactive resources.

Thanks!