title: How do I add trackable to an existing Devise setup?
body: <p>Im trying to get the last sign in date time in RoR application using Devise gem. In one of my migration files I noticed the <code># t.datetime :last_sign_in_at</code> field among others:</p>
  
  <pre><code>## Trackable
    # t.integer  :sign_in_count, default: 0, null: false
    # t.datetime :current_sign_in_at
    # t.datetime :last_sign_in_at
    # t.string   :current_sign_in_ip
    # t.string   :last_sign_in_ip
  </code></pre>
  
  <p>So the question is: how to activate this field for my users to be able to call it later in my app? Should I just uncomment that?</p>