update documentation of badges

[maelle]

Fix r-universe-org/help#559

@jeroen I'll try making a PR to edit https://r-lib.r-universe.dev/badges

[maelle]

I'm stuck: I found badges.pug but I'm not sure how pkgdata is created (maybe it even already contains the status?)

[jeroen]

I forgot to mention I also moved the version badge in the API 🙈 but with a permanent redirect so the old location also works.

I'm stuck: I found badges.pug but I'm not sure how pkgdata is created (maybe it even already contains the status?)

We should document also how the express routing works. Perhaps this can be another chapter in #42. (the badges api is routed here: https://github.com/r-universe-org/frontend/blob/main/routes/universe.js#L134-L161)