Add use_r_universe_badge()

[olivroy]

FIx #1883

It has limitations, in the sense that it doesn't verify that the repo actually exists. It would also be great to add the r-universe installation options too.

I could add this to the badge with ui_code()

install.packages('{pkg}', repos = c('https://{org}.r-universe.dev', 'https://cloud.r-project.org'))

It worked out of the box with usethis

implementation considerations

• marked it as experimental
• requires a (github?) url in DESCRIPTION, or can probably manage with only git remote.
• Assumes r-universe is set up (which is true for CRAN packages that have a repo link in DESCRIPTION), although it would probably be great to check if R-universe is set-up and nudge towards r-universe help, but that seems out of scope for this PR.
• If the repo name is different than packages name, it doesn't affect the r-universe url. So rstudio/pins-r still has the
• Doesn't currently care for a r-universe.dev link in description, (probably should though, but I didn't want the function to get too complicated)
• Added an example for how to manually setup a r-universe badge in use_badge()

If you want, you can let me know what you think @jeroen. And you'd probably best to implement this function.

ideas

A browse_r_universe() similar to browse_github() would probably be useful and easy to implement + the badge could build on top of this.

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