Feature Request: Add support to install packages from r-universe

Integration with https://r-universe.dev/ would be excellent. I'd love to be able to do something like:

```r
remotes::install_runiverse("maelle/goodpress")

# equivalent(-ish) to
remotes::install_cran("goodpress", repos = "https://maelle.r-universe.dev")
```

A similar syntax for `Remotes` would also be helpful:

```
Remotes:
	runiverse::maelle/goodpress
```