Add it to your Gemfile:
gem 'astrochimp'
Run the following command to install it:
bundle install
Copy the migrations over:
rake astrochimp:install:migrations
rake db:migrate
Now edit config/astrochimp.yml and add your MailChimp API Key and List ID.
Your app is now chimpified. Start your server and navigate to the root:
rails s
open http://localhost:3000