title: How to add callback after registration with Rails3 and Devise
body: <p>How to add a callback to create an account for the registered user.</p>
  
  <p>Devise files (registrations_controller.rb) are under controllers/devise
  My user model has has_many :accounts relationship (and the account model has belongs_to :user)</p>
  
  <p>First I don't know where to add the callback (what file?)</p>
  
  <p>Then, how to automatically create a new account with the right user_id of the registered user?</p>
  
  <p>Thanks in advance.</p>