docs: add rg9400 as a contributor (#703)

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

.all-contributorsrc

@@ -693,6 +693,15 @@
       "contributions": [
         "doc"
       ]
+    },
+    {
+      "login": "rg9400",
+      "name": "rg9400",
+      "avatar_url": "https://avatars2.githubusercontent.com/u/39887349?v=4",
+      "profile": "https://github.com/rg9400",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -162,6 +162,7 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
     <td align="center"><a href="http://www.gridgeo.com"><img src="https://avatars1.githubusercontent.com/u/671887?v=4" width="100px;" alt=""/><br /><sub><b>Chander Ganesan</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=chander" title="Documentation">📖</a></td>
     <td align="center"><a href="https://github.com/yrien30"><img src="https://avatars1.githubusercontent.com/u/26816162?v=4" width="100px;" alt=""/><br /><sub><b>yrien30</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=yrien30" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/ksurl"><img src="https://avatars1.githubusercontent.com/u/1371562?v=4" width="100px;" alt=""/><br /><sub><b>ksurl</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=ksurl" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/rg9400"><img src="https://avatars2.githubusercontent.com/u/39887349?v=4" width="100px;" alt=""/><br /><sub><b>rg9400</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=rg9400" title="Code">💻</a></td>
   </tr>
 </table>