How do I get ‘puma’ to start, automatically, when I run `rails server` (like Thin does)

After some digging, I’ve found this answer: https://stackoverflow.com/a/14911994/604526

To make Puma the default, paste this code into script/rails above require ‘rails/commands’:

require 'rack/handler'
Rack::Handler::WEBrick = Rack::Handler.get(:puma)

Puma is the default server now if you use rails s

rails s
=> Booting Puma
=> Rails 3.2.12 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Connecting to database specified by database.yml
Puma 1.6.3 starting...
* Min threads: 0, max threads: 16
* Environment: development
* Listening on tcp://0.0.0.0:3000

Rails 4

With Rails 4 you simply have to add the puma-gem to the Gemfile. (Tested with Rails 4.0.2 and Puma 2.6.0)