title: wkhtmltopdf, how to use relative path images when use stdin
body: <p>files: sample.html, image.jpg.</p>
  
  <p>sample.html:</p>
  
  <pre><code>...
  &lt;img src='image.jpg'/&gt;
  ...
  </code></pre>
  
  <p>cmd:</p>
  
  <p><code>cat sample.html | wkhtmltopdf - output.pdf</code></p>
  
  <p>image can't display.</p>