title: How to add button to ActiveAdmin's index page
body: <p>I created a collection action for ActiveAdmin rescource and want to link to it from the resource index page.</p>
  
  <p>But how do I customize the resource index page?</p>
  
  <p>The manual gives some options, but none to add html / buttons on the page (or I cannot see where).</p>
  
  <p><a href="http://activeadmin.info/docs/3-index-pages.html" rel="noreferrer">http://activeadmin.info/docs/3-index-pages.html</a></p>