title: How to allow users to view individual instances of a resource but not the index with CanCan?
body: <p>I'll try to be more clear than the title. I want users to be able to view all individual widgets which might be at the following URLs:</p>
  
  <pre><code>/widgets/2
  /widgets/3
  /widgets/45
  </code></pre>
  
  <p>But I don't want users to view the entire index:</p>
  
  <pre><code>/widgets
  </code></pre>
  
  <p>I know I can check this in the controller or even in the view for <code>index</code> and <code>show</code>, but I'm looking for a simpler way I can add this in the <code>Ability.rb</code> file:</p>
  
  <pre><code>can :read, Widget
  </code></pre>
  
  <p>Of course, that will allow users to view the index too...</p>