title: Drop-down menu for active admin resource
body: <p>I'm trying to create a drop down menu in active admin's navigation. The docs: </p>
  
  <p><a href="https://activeadmin.info/2-resource-customization.html#customize-the-menu" rel="nofollow noreferrer">https://activeadmin.info/2-resource-customization.html#customize-the-menu</a></p>
  
  <p>says all I need to do is create the menu: </p>
  
  <pre><code>    config.namespace :admin do |admin|
        admin.build_menu do |menu|
          menu.add label: 'example', priority: 0
        end
      end
  </code></pre>
  
  <p>then add that menu as the parent of the resource: </p>
  
  <pre><code>menu parent: 'example'
  </code></pre>
  
  <p>But that doesn't work for me.</p>
  
  <p>The only thing that has thus far is this:</p>
  
  <pre><code>    config.namespace :admin do |admin|
        admin.build_menu do |menu|
          menu.add label: 'Appointment', priority: 0, html_options: { target: :blank } do |item|
            item.add label: 'Appointment',  url: '/admin/appointments'
            item.add label: 'AppointmentCommunication',  url: '/admin/appointment_communications'
          end
        end
      end
  </code></pre>
  
  <p>With menu: false in the actual resource file.</p>
  
  <p>But that's pretty messy, and not well organized. I was hoping to have a simpler way of making the menus. But maybe I'm just missing something. </p>
  
  <p>Note: I did try to name the menu something that wasn't the name of one of the resources but alas no changes. Additionally, I tried moving the two resources - Appointment and AppointmentCommunication - into a folder called Appointment but obviously that didn't work. </p>
  
  <p>Any thoughts on this would be appreciated.</p>