title: How to include markdown file (md) inside mdx file
body: <p>plain.md</p>
  <pre><code># plain markdown
  </code></pre>
  <p>some.mdx</p>
  <pre><code># some mdx file
  
  include './plain.md'
  </code></pre>
  <p>Result file</p>
  <pre><code># some mdx file
  
  # plain markdown
  </code></pre>
  <p>How to do something like this with <a href="https://github.com/mdx-js/mdx" rel="nofollow noreferrer">mdxjs</a>?</p>