title: HowTo add a required indicator to paper-input
body: <p>Given the paper-input</p>
  
  <pre><code>&lt;paper-input 
    floatingLabel label="Type only numbers... (floating)" 
    validate="^[0-9]*$" error="Input     is not a number!"&gt;
  &lt;/paper-input&gt;
  </code></pre>
  
  <p>How do I add some indication that the field is required to the user.</p>