Twitter Bootstrap 3.3.4 on Rails 4.2.1

1. Add : gem 'bootstrap-sass', '~> 3.3.4' to Gemfile.
2. Run bundle
3. Rename application.css to application.scss
4. Copy this to application.scss

// "bootstrap-sprockets" must be imported before "bootstrap" and "bootstrap/variables"
@import "bootstrap-sprockets";
@import "bootstrap";