Simply specify this gem as a dependency of your application that also contains Forem:
gem 'forem', :git => "git://github.com/radar/forem"
gem 'forem-redcarpet', :git => "git://github.com/radar/forem-redcarpet"
The code will do the rest!
Comes with syntax highlighting provided by Redcarpet, however you'll need to generate the CSS yourself with this lovely command:
Pygments.css
Enjoy!