title: Adding the 'required' attribute with DropDownListFor
body: <p>I have this:</p>
  
  <pre><code>@Html.DropDownListFor(x =&gt; x.SelectedValue, new SelectList(Model.SomeList, "Value", "Text"))
  </code></pre>
  
  <p>And would like it to be rendered as this:</p>
  
  <pre><code>&lt;select required&gt;
      &lt;option&gt;...&lt;/option&gt;
      ...
  </code></pre>
  
  <p>How would I do this?</p>