RMagick doc's as html are in /usr/share/RMagick. They should be in /usr/share/doc/rmagick-$(version). In /usr/share/doc/rmagick-$(version) are some bzip'd examples. I have dev-ruby/rmagic-2.8.0
Thanks for reporting this. I've now fixed this for dev-ruby/rmagic-2.8.0-r1.