docs: update README.md

Author: allcontributors[bot]

README.md

@@ -480,6 +480,13 @@ See [ARCHITECTURE.md](ARCHITECTURE.md) for a detailed breakdown of **gh-stack**'
 <!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
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+<table>
+  <tbody>
+    <tr>
+      <td align="center" valign="top" width="14.28%"><a href="https://github.com/mvanhorn"><img src="https://avatars.githubusercontent.com/u/455140?v=4?s=100" width="100px;" alt="Matt Van Horn"/><br /><sub><b>Matt Van Horn</b></sub></a><br /><a href="#code-mvanhorn" title="Code">💻</a></td>
+    </tr>
+  </tbody>
+</table>
 
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