docs: add Arcath as a contributor (#13)

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

Author: allcontributors[bot]

.all-contributorsrc

@@ -42,7 +42,8 @@
         "code",
         "test",
         "ideas",
-        "review"
+        "review",
+        "doc"
       ]
     },
     {

README.md

@@ -330,7 +330,7 @@ Thanks goes to these people ([emoji key][emojis]):
   <tr>
     <td align="center"><a href="https://kentcdodds.com"><img src="https://avatars.githubusercontent.com/u/1500684?v=3?s=100" width="100px;" alt=""/><br /><sub><b>Kent C. Dodds</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/commits?author=kentcdodds" title="Code">💻</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=kentcdodds" title="Documentation">📖</a> <a href="#infra-kentcdodds" title="Infrastructure (Hosting, Build-Tools, etc)">🚇</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=kentcdodds" title="Tests">⚠️</a></td>
     <td align="center"><a href="https://github.com/benwis"><img src="https://avatars.githubusercontent.com/u/6953353?v=4?s=100" width="100px;" alt=""/><br /><sub><b>benwis</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/issues?q=author%3Abenwis" title="Bug reports">🐛</a> <a href="https://github.com/kentcdodds/mdx-bundler/pulls?q=is%3Apr+reviewed-by%3Abenwis" title="Reviewed Pull Requests">👀</a></td>
-    <td align="center"><a href="https://arcath.net"><img src="https://avatars.githubusercontent.com/u/19609?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Adam Laycock</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/commits?author=Arcath" title="Code">💻</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=Arcath" title="Tests">⚠️</a> <a href="#ideas-Arcath" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/kentcdodds/mdx-bundler/pulls?q=is%3Apr+reviewed-by%3AArcath" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://arcath.net"><img src="https://avatars.githubusercontent.com/u/19609?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Adam Laycock</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/commits?author=Arcath" title="Code">💻</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=Arcath" title="Tests">⚠️</a> <a href="#ideas-Arcath" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/kentcdodds/mdx-bundler/pulls?q=is%3Apr+reviewed-by%3AArcath" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=Arcath" title="Documentation">📖</a></td>
     <td align="center"><a href="http://wooorm.com"><img src="https://avatars.githubusercontent.com/u/944406?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Titus</b></sub></a><br /><a href="#ideas-wooorm" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/kentcdodds/mdx-bundler/pulls?q=is%3Apr+reviewed-by%3Awooorm" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=wooorm" title="Code">💻</a></td>
   </tr>
 </table>