agda-categories should list compatibility versions on README

[Boarders]

Similar to the cubical library it would be nice if agda-categories listed the compatibilities of the versions of agda it works with. See the compiling and installing section of this README: https://github.com/agda/cubical

[JacquesCarette]

Agreed. I'd welcome a PR that documented that. [I just know I might not get the time to do this for a couple of weeks.]