title: radio_button in edit form
body: <p>I have a standard scaffold.  In my edit action it looks like the value set with the radio button on the create action is not shown.  How do I get the form to fill in the set value? </p>
  
  <pre><code>&lt;%= form_for([@rating]) do |f| %&gt;
  
  &lt;%= f.radio_button :environment, 1 %&gt;
  &lt;%= f.radio_button :environment, 2 %&gt;
  &lt;%= f.radio_button :environment, 3 %&gt;
  </code></pre>