Badge for r-universe?

[coatless]

With an up-tick of usage with r-universe, would a PR to add an r-universe badge to the README of a project be of interest?

e.g.

usethis::use_r_universe_badge()

would generate:

[![r-universe](https://r-lib.r-universe.dev/badges/usethis)](https://r-lib.r-universe.dev/usethis)

That renders as:

Note: One downside would be the setup procedure requires a manual opt-in for folks new to the r-universe.

https://github.com/apps/r-universe/installations/new

[hadley]

I think we'd accept a PR for this. Maybe just assume the caller has already opted-in?