title: .dockerignore all subfolders but not files in the folder itself
body: <p>I've got a folder structure like below. I want to ignore all subfolders (and all their content) of <code>.git</code> but include all files which are directly in <code>.git</code> (e.g. FETCH_HEAD and HEAD).</p>
  
  <p>How do I write that in the <code>.dockerignore</code> file.</p>
  
  <pre><code>.git
  ├── COMMIT_EDITMSG
  ├── FETCH_HEAD
  ├── HEAD
  ├── description
  ├── hooks
  │   ├── applypatch-msg.sample
  │   ├── commit-msg.sample
  │   ├── post-update.sample
  │   ├── pre-applypatch.sample
  </code></pre>