title: Using rolify with existing models
body: <p>I have a role model all ready in my application.</p>
  
  <pre><code>class Role &lt; ActiveRecord::Base
    belongs_to :user
    belongs_to :department
  end
  </code></pre>
  
  <p>How can I use <a href="https://github.com/RolifyCommunity/rolify" rel="nofollow noreferrer">https://github.com/RolifyCommunity/rolify</a> given that I wont be able to generate and run the migration file ?</p>