docs: add tammert as a contributor (#538)

* docs: update README.md [skip ci]

* docs: update .all-contributorsrc [skip ci]

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

.all-contributorsrc

@@ -564,6 +564,15 @@
       "contributions": [
         "doc"
       ]
+    },
+    {
+      "login": "tammert",
+      "name": "Sebastiaan Tammer",
+      "avatar_url": "https://avatars0.githubusercontent.com/u/8885250?v=4",
+      "profile": "https://github.com/tammert",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -147,6 +147,7 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
     <td align="center"><a href="https://rubyroidlabs.com/"><img src="https://avatars2.githubusercontent.com/u/624999?v=4" width="100px;" alt=""/><br /><sub><b>Valentine Zavadsky</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=Saicheg" title="Code">💻</a> <a href="https://github.com/containrrr/watchtower/commits?author=Saicheg" title="Documentation">📖</a> <a href="https://github.com/containrrr/watchtower/commits?author=Saicheg" title="Tests">⚠️</a></td>
     <td align="center"><a href="https://github.com/bopoh24"><img src="https://avatars2.githubusercontent.com/u/4086631?v=4" width="100px;" alt=""/><br /><sub><b>Alexander Voronin</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=bopoh24" title="Code">💻</a> <a href="https://github.com/containrrr/watchtower/issues?q=author%3Abopoh24" title="Bug reports">🐛</a></td>
     <td align="center"><a href="http://www.teqneers.de"><img src="https://avatars0.githubusercontent.com/u/788989?v=4" width="100px;" alt=""/><br /><sub><b>Oliver Mueller</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=ogmueller" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/tammert"><img src="https://avatars0.githubusercontent.com/u/8885250?v=4" width="100px;" alt=""/><br /><sub><b>Sebastiaan Tammer</b></sub></a><br /><a href="https://github.com/containrrr/watchtower/commits?author=tammert" title="Code">💻</a></td>
   </tr>
 </table>