title: Repository commit referenced in another repo as directory
body: <p>I was looking at the code in a GitHub repository when I found the following:</p>
  <pre><code>&lt;repo name&gt; @ &lt;commit hash&gt;
  </code></pre>
  <p><a href="https://i.stack.imgur.com/mY8KN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mY8KN.png" alt="enter image description here" /></a></p>
  <p>I have used GitHub for quite some while now but never saw something like this. What is it and how do I go about doing this in my own repositories?</p>
  <p>Thanks in advance</p>