http://ylan.segal-family.com/blog/2013/01/07/code-navigation-in-sublime-text-2-with-ctags/

ctags.rb

#!/usr/bin/env ruby

# Generate project ctags
system("find . -name '*.rb' | ctags -f .tags -L -")

# Generate gem ctags
if File.exist?('./Gemfile')
  require 'bundler'
  paths = Bundler.load.specs.map(&:full_gem_path).join(' ')
  system("ctags -R -f .gemtags #{paths}")
end