To install with Git:
mkdir -p ~/Library/Application\ Support/TextMate/Bundles
cd ~/Library/Application\ Support/TextMate/Bundles
git clone git://github.com/drnic/ruby-on-rails-tmbundle.git "Ruby on Rails.tmbundle"
osascript -e 'tell app "TextMate" to reload bundles'
To install without Git:
mkdir -p ~/Library/Application\ Support/TextMate/Bundles
cd ~/Library/Application\ Support/TextMate/Bundles
wget http://github.com/drnic/ruby-on-rails-tmbundle/tarball/master
tar zxf drnic-ruby-on-rails-tmbundle*.tar.gz
rm drnic-ruby-on-rails-tmbundle*.tar.gz
mv drnic-ruby-on-rails-tmbundle* "Ruby on Rails.tmbundle"
osascript -e 'tell app "TextMate" to reload bundles'
Ruby 1.8.7 or greater is required.