title: How can I exclude a sub-directory with a .dockerignore file
body: <p>I want to exclude a sub-directory using a <code>.dockerignore</code> file, but I don't know what the syntax should be, and there are no examples anywhere.</p>
  
  <p>I have a sub-directory <code>vendor/bundle</code>.</p>
  
  <p>I've put</p>
  
  <p><code>vendor/bundle</code> in the <code>.dockerignore</code> file. Also <code>vendor/bundle/</code> and <code>/vendor/bundle</code> but none of them seem to work.</p>
  
  <p>(Also, the <code>.dockerignore</code> file is being found, but just not working.)</p>