Provide info on typelevel project membership

[ceedubs]

We have this handy writeup regarding typelevel membership: https://github.com/typelevel/general/blob/master/governance/membership.md

However I don't see any way to get to this information from the typelevel website. People browsing the list of typelevel projects may wonder "how do I get my project on this list?". I think that it would be nice to at least link to this document from the website.

More generally it also might make sense for the website to link to https://github.com/typelevel/general . It's possible that it already does that somewhere and I'm missing it, but if so it's not very prominent.

[larsrh]

PRs welcome 😄