title: Mailchimp - add checkbox to list fields
body: <p>I started to use mailchimp and finds it very helpful.</p>
  
  <p>However, I would like to add to my list a checkbox field, and cannot find it.
  I neither find a way to give a default value (for example, I could think of a non-elegant way to use a radio button instead of a checkbox...).</p>
  
  <p>Help please? Thanks!</p>