docs: add petergtz as a contributor for code, doc (#521)

* docs: update CONTRIBUTING.md [skip ci]

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

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

.all-contributorsrc

@@ -107,6 +107,16 @@
         "code"
       ]
     },
+    {
+      "login": "petergtz",
+      "name": "Peter Götz",
+      "avatar_url": "https://avatars.githubusercontent.com/u/3618401?v=4",
+      "profile": "https://github.com/petergtz",
+       "contributions": [
+        "code",
+        "doc"
+      ]
+    },
     {
       "login": "bloebp",
       "name": "Patrick Blöbaum",

CONTRIBUTING.md

@@ -25,6 +25,7 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
     <td align="center"><a href="https://github.com/EgorKraevTransferwise"><img src="https://avatars.githubusercontent.com/u/62890791?v=4?s=100" width="100px;" alt=""/><br /><sub><b>EgorKraevTransferwise</b></sub></a><br /><a href="https://github.com/py-why/dowhy/commits?author=EgorKraevTransferwise" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/ryanrussell"><img src="https://avatars.githubusercontent.com/u/523300?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ryan Russell</b></sub></a><br /><a href="https://github.com/py-why/dowhy/commits?author=ryanrussell" title="Documentation">📖</a></td>
     <td align="center"><a href="https://github.com/MichaelMarien"><img src="https://avatars.githubusercontent.com/u/13829139?v=4?s=100" width="100px;" alt=""/><br /><sub><b>MichaelMarien</b></sub></a><br /><a href="https://github.com/py-why/dowhy/commits?author=MichaelMarien" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/petergtz"><img src="https://avatars.githubusercontent.com/u/3618401?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Peter Götz</b></sub></a><br /><a href="https://github.com/py-why/dowhy/commits?author=petergtz" title="Code">💻</a> <a href="https://github.com/py-why/dowhy/commits?author=petergtz" title="Documentation">📖</a></td>
     <td align="center"><a href="https://github.com/bloebp"><img src="https://avatars.githubusercontent.com/u/51325689?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Patrick Blöbaum</b></sub></a><br /><a href="https://github.com/py-why/dowhy/commits?author=bloebp" title="Code">💻</a> <a href="https://github.com/py-why/dowhy/commits?author=bloebp" title="Documentation">📖</a></td>
   </tr>
 </table>