Link to the new cats-friendly badge

[kailuowang]

Add to README the links to the newly added "Cats Friendly" badges (see PR below) so that people can start to use.

#2524

The urls will be https://typelevel.org/cats/img/XXXX.svg

[calvinbrown085]

@kailuowang Hi! I'm happy to pick this one up, is there a specific place in the README https://github.com/typelevel/cats#libraries-with-more-specific-uses
maybe at the bottom of this page?

The full-size Cats logo is available for use for Cats related projects, contents, souvenirs, etc.

Possibly underneath this? I can create a quick PR to see what it looks like

[rossabaker]

I did it for http4s like this. I'll bet it can be done better, but there's some prior art.

[calvinbrown085]

Oh nice! I'm trying to think of a good way to advertise to other repositories that the badge is available?

I'm still thinking about that section I mentioned. I might be off in what we are trying to do here though. Happy to discuss!

[rossabaker]

Oh, you're right. I thought it was about adding it to our own readme. Though it would be good to have a markdown snippet that people can just copy and paste and work in most readmes.

[ceedubs]

Resolved by #2554