docs: update README.md [skip ci]

Former-commit-id: ca2e12c

README.md

@@ -181,6 +181,7 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
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     <td align="center"><a href="https://www.evetion.nl"><img src="https://avatars0.githubusercontent.com/u/8655030?v=4" width="100px;" alt=""/><br /><sub><b>Maarten Pronk</b></sub></a><br /><a href="#infra-evetion" title="Infrastructure (Hosting, Build-Tools, etc)">🚇</a></td>
+    <td align="center"><a href="https://github.com/visr"><img src="https://avatars1.githubusercontent.com/u/4471859?v=4" width="100px;" alt=""/><br /><sub><b>Martijn Visser</b></sub></a><br /><a href="https://github.com/JuliaEarth/GeoStats.jl/commits?author=visr" title="Code">💻</a></td>
   </tr>
 </table>