title: Importing propTypes from external file in React Styleguidist
body: <p>I'd like to reuse a common set of PropTypes across several components. Something like:</p>
  
  <pre><code>const textProps = {
    /** Header text */
    children: PropTypes.node.isRequired,
    /** Weight of the text */
    weight: PropTypes.oneOf(['thin', 'normal', 'semibold', 'bold']),
  }
  </code></pre>
  
  <p>I've added this object to a file and am exporting it as a named export <code>textProps</code>. </p>
  
  <p>I then import it into a component file as:</p>
  
  <pre><code>import { textProps } from 'path/to/textProps'
  </code></pre>
  
  <p>And the component file uses <code>styled-components</code> to define a component:</p>
  
  <pre><code>const H1 = styled.h1`
    font-size: "50px"
  `;
  
  H1.propTypes = textProps;
  </code></pre>
  
  <p>The problem is the 'Props &amp; Methods' section isn't displayed in the Styleguidist guide when <code>textProps</code> is imported.</p>
  
  <p>When I define <code>textProps</code> within the <code>H1</code> file it works as expected.</p>
  
  <p>Is there a way to define a common set of PropTypes, import them into a component, and have them appear in the Styleguidist guide?</p>