docs: add jamsinclair as a contributor (#555)

Author: allcontributors[bot]

.all-contributorsrc

@@ -889,6 +889,16 @@
         "code",
         "test"
       ]
+    },
+    {
+      "login": "jamsinclair",
+      "name": "Jamie",
+      "avatar_url": "https://avatars0.githubusercontent.com/u/5964236?v=4",
+      "profile": "https://jamie.tokyo",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "repoHost": "https://github.com"

README.md

@@ -246,6 +246,7 @@ Thanks goes to these people ([emoji key][emojis]):
     <td align="center"><a href="https://github.com/airjp73"><img src="https://avatars2.githubusercontent.com/u/25882770?v=4" width="100px;" alt=""/><br /><sub><b>Aaron Pettengill</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=airjp73" title="Code">💻</a> <a href="https://github.com/testing-library/dom-testing-library/commits?author=airjp73" title="Tests">⚠️</a></td>
     <td align="center"><a href="http://kwboyd.com"><img src="https://avatars0.githubusercontent.com/u/13855750?v=4" width="100px;" alt=""/><br /><sub><b>Kate W. Boyd</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=kwboyd" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/rahulchavan30"><img src="https://avatars2.githubusercontent.com/u/5296464?v=4" width="100px;" alt=""/><br /><sub><b>Rahul Suryakanth</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=rahulchavan30" title="Code">💻</a> <a href="https://github.com/testing-library/dom-testing-library/commits?author=rahulchavan30" title="Tests">⚠️</a></td>
+    <td align="center"><a href="https://jamie.tokyo"><img src="https://avatars0.githubusercontent.com/u/5964236?v=4" width="100px;" alt=""/><br /><sub><b>Jamie</b></sub></a><br /><a href="https://github.com/testing-library/dom-testing-library/commits?author=jamsinclair" title="Code">💻</a> <a href="https://github.com/testing-library/dom-testing-library/commits?author=jamsinclair" title="Tests">⚠️</a></td>
   </tr>
 </table>