docs: add matthewfeickert as a contributor for maintenance (#1086)

* 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

@@ -257,6 +257,15 @@
         "code",
         "test"
       ]
+    },
+    {
+      "login": "matthewfeickert",
+      "name": "Matthew Feickert",
+      "avatar_url": "https://avatars.githubusercontent.com/u/5142394?v=4",
+      "profile": "http://www.matthewfeickert.com/",
+      "contributions": [
+        "maintenance"
+      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -283,6 +283,7 @@ Thanks especially to the gracious help of Awkward Array contributors (including
     <td align="center"><a href="https://github.com/HenryDayHall"><img src="https://avatars.githubusercontent.com/u/12996763?v=4?s=100" width="100px;" alt=""/><br /><sub><b>HenryDayHall</b></sub></a><br /><a href="https://github.com/scikit-hep/awkward-1.0/commits?author=HenryDayHall" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/agoose77"><img src="https://avatars.githubusercontent.com/u/1248413?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Angus Hollands</b></sub></a><br /><a href="https://github.com/scikit-hep/awkward-1.0/commits?author=agoose77" title="Tests">⚠️</a> <a href="https://github.com/scikit-hep/awkward-1.0/commits?author=agoose77" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/ioanaif"><img src="https://avatars.githubusercontent.com/u/9751871?v=4?s=100" width="100px;" alt=""/><br /><sub><b>ioanaif</b></sub></a><br /><a href="https://github.com/scikit-hep/awkward-1.0/commits?author=ioanaif" title="Code">💻</a> <a href="https://github.com/scikit-hep/awkward-1.0/commits?author=ioanaif" title="Tests">⚠️</a></td>
+    <td align="center"><a href="http://www.matthewfeickert.com/"><img src="https://avatars.githubusercontent.com/u/5142394?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Matthew Feickert</b></sub></a><br /><a href="#maintenance-matthewfeickert" title="Maintenance">🚧</a></td>
   </tr>
 </table>