Add Rocky 8 information to INSTALL.md
Add Rocky 8 information to INSTALL.md

We have official releases for it, now available via ponyup.

dipinhora/ponyc,jemc/ponyc,jemc/ponyc,sgebbie/ponyc,sgebbie/ponyc,ponylang/ponyc,dipinhora/ponyc,jemc/ponyc,sgebbie/ponyc,sgebbie/ponyc,dipinhora/ponyc,sgebbie/ponyc,ponylang/ponyc,ponylang/ponyc