Mark the repo as archived

[cooljeanius]

In ccef38c a shutdown notice was added. However, this repo is still open, meaning that people can still open new issues and PRs against it, and all the old issues still show up in people's issue lists. If nothing further will be done with this repo, then it should be marked as "archived", so that people don't get confused and think that this repo is still active. Specifically, I mean using the "Archive this repository" button under the "Danger Zone" under repository settings: