title: Add internal links to a MARP presentation
body: <p>I have a basic MARP presentation, <a href="https://github.com/marp-team/marp" rel="nofollow noreferrer">https://github.com/marp-team/marp</a>. I would like to add links to emulate footnotes or references. Is this possible, what about the PDF export?</p>
  <pre><code>Some text with source. [1]
  </code></pre>
  <p>The &quot;1&quot; should link to another slide:</p>
  <pre><code>1. some description
  </code></pre>
  <p>PS
  I do not have enough reputation to create the <code>marp</code> tag for this question, as described by the MARP Readme.</p>