docs: add karthick3018 as a contributor (#785)

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

Author: allcontributors[bot]

.all-contributorsrc

@@ -1176,6 +1176,15 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "karthick3018",
+      "name": "Karthick Raja",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/47154512?v=4",
+      "profile": "https://github.com/karthick3018",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -596,6 +596,7 @@ Thanks goes to these people ([emoji key][emojis]):
     <td align="center"><a href="https://antonhalim.com"><img src="https://avatars1.githubusercontent.com/u/10498035?v=4" width="100px;" alt=""/><br /><sub><b>Anton Halim</b></sub></a><br /><a href="https://github.com/testing-library/react-testing-library/commits?author=antonhalim" title="Documentation">📖</a></td>
     <td align="center"><a href="http://artmalko.ru"><img src="https://avatars0.githubusercontent.com/u/1823689?v=4" width="100px;" alt=""/><br /><sub><b>Artem Malko</b></sub></a><br /><a href="https://github.com/testing-library/react-testing-library/commits?author=artem-malko" title="Code">💻</a></td>
     <td align="center"><a href="http://gerritalex.de"><img src="https://avatars1.githubusercontent.com/u/29307652?v=4" width="100px;" alt=""/><br /><sub><b>Gerrit Alex</b></sub></a><br /><a href="https://github.com/testing-library/react-testing-library/commits?author=ljosberinn" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/karthick3018"><img src="https://avatars1.githubusercontent.com/u/47154512?v=4" width="100px;" alt=""/><br /><sub><b>Karthick Raja</b></sub></a><br /><a href="https://github.com/testing-library/react-testing-library/commits?author=karthick3018" title="Code">💻</a></td>
   </tr>
 </table>