title: How to append "optional" text to form input label
body: <p>I'm new to Angular 2 and trying to append a text to form inputs that are optionals.</p>
  
  <p>Something like this (<code>app-optional</code>):</p>
  
  <pre><code>&lt;div class="form-group"&gt;
    &lt;label app-optional&gt;
      Name
      ... input here ...
    &lt;/label&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Which should result in:</p>
  
  <p>Name <em>- optional</em></p>
  
  <p>How could I achieve this? Or could you suggest a better way?</p>