What the badge should be granted for: reviewing packages
Badge description (like "You added a co-maintainer to a package. BFF!"): You reviewed a package. Keep Fedora growing!

Anything else we need to know:

Might want a variant with 1 / 10 / 100 reviews or so.

sgallagh suggested this in the FESCo candidate interview (http://fedoramagazine.org/fesco-elections-interview-stephen-gallagher-sgallagh/), and I think it's a great idea.