docs: add kgregory as a contributor (#653)

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

Author: allcontributors[bot]

.all-contributorsrc

@@ -1075,6 +1075,16 @@
         "code",
         "test"
       ]
+    },
+    {
+      "login": "kgregory",
+      "name": "Ken Gregory",
+      "avatar_url": "https://avatars0.githubusercontent.com/u/3155127?v=4",
+      "profile": "http://kengregory.com",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "repoHost": "https://github.com"

README.md

@@ -271,6 +271,7 @@ Thanks goes to these people ([emoji key][emojis]):
     <td align="center"><a href="https://github.com/mdjastrzebski"><img src="https://avatars2.githubusercontent.com/u/6368606?v=4" width="100px;" alt=""/><br /><sub><b>Maciej Jastrzebski</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/issues?q=author%3Amdjastrzebski" title="Bug reports">🐛</a></td>
     <td align="center"><a href="https://commonlit.org"><img src="https://avatars3.githubusercontent.com/u/319471?v=4" width="100px;" alt=""/><br /><sub><b>Geoff Harcourt</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=geoffharcourt" title="Code">💻</a></td>
     <td align="center"><a href="http://www.joshuakgoldberg.com"><img src="https://avatars1.githubusercontent.com/u/3335181?v=4" width="100px;" alt=""/><br /><sub><b>Josh Goldberg</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=JoshuaKGoldberg" title="Code">💻</a> <a href="https://github.com/testing-library/dom-testing-library/commits?author=JoshuaKGoldberg" title="Tests">⚠️</a></td>
+    <td align="center"><a href="http://kengregory.com"><img src="https://avatars0.githubusercontent.com/u/3155127?v=4" width="100px;" alt=""/><br /><sub><b>Ken Gregory</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=kgregory" title="Code">💻</a> <a href="https://github.com/testing-library/dom-testing-library/commits?author=kgregory" title="Tests">⚠️</a></td>
   </tr>
 </table>