title: make an input field required in ember.js
body: <p>I know there is a way in plain html to require the field have some kind of value. I believe it's 'input required'.
  However, I'm not sure how to accomplish this in ember using handlebars. I've tried this but it was unsuccessful:</p>
  
  <pre><code>{{input required value=tax class="form-control" placeholder="State Tax"}}
  </code></pre>
  
  <p>Thanks in advance.</p>