Because Ruby & Gems suck in a general, we should add a Gemfile (maybe Gemfile.lock as well?) and recommend using Bundler & bundle exec cap... for everything:

source 'https://rubygems.org'

gem 'capistrano', '~> 2.15'
gem 'capistrano-ext', '~> 1.2.1'
gem 'colored', '~> 1.2'
gem 'sass', '~> 3.2.14'