docs: update README.md [skip ci]

Author: allcontributors[bot]

README.md

@@ -14,9 +14,7 @@
 [![black code style](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)
 
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-
-[![All Contributors](https://img.shields.io/badge/all_contributors-49-orange.svg)](#-contributors)
-
+[![All Contributors](https://img.shields.io/badge/all_contributors-50-orange.svg)](#-contributors)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 </div>
@@ -246,6 +244,9 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/awadell1"><img src="https://avatars.githubusercontent.com/u/5857298?v=4?s=100" width="100px;" alt="Alex Wadell"/><br /><sub><b>Alex Wadell</b></sub></a><br /><a href="https://github.com/pybamm-team/PyBaMM/commits?author=awadell1" title="Code">💻</a> <a href="https://github.com/pybamm-team/PyBaMM/commits?author=awadell1" title="Tests">⚠️</a> <a href="https://github.com/pybamm-team/PyBaMM/commits?author=awadell1" title="Documentation">📖</a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/iatzak"><img src="https://avatars.githubusercontent.com/u/112731474?v=4?s=100" width="100px;" alt="iatzak"/><br /><sub><b>iatzak</b></sub></a><br /><a href="https://github.com/pybamm-team/PyBaMM/commits?author=iatzak" title="Documentation">📖</a> <a href="https://github.com/pybamm-team/PyBaMM/issues?q=author%3Aiatzak" title="Bug reports">🐛</a> <a href="https://github.com/pybamm-team/PyBaMM/commits?author=iatzak" title="Code">💻</a></td>
     </tr>
+    <tr>
+      <td align="center" valign="top" width="14.28%"><a href="https://github.com/ayeankit"><img src="https://avatars.githubusercontent.com/u/72691866?v=4?s=100" width="100px;" alt="Ankit Kumar"/><br /><sub><b>Ankit Kumar</b></sub></a><br /><a href="https://github.com/pybamm-team/PyBaMM/commits?author=ayeankit" title="Code">💻</a></td>
+    </tr>
   </tbody>
 </table>