add RubendeBruin as a contributor for doc (#810)

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

.all-contributorsrc

@@ -915,7 +915,8 @@
       "avatar_url": "https://avatars.githubusercontent.com/u/34062862?v=4",
       "profile": "https://rdbr.nl",
       "contributions": [
-        "code"
+        "code",
+        "doc"
       ]
     }
   ],

README.md

@@ -243,7 +243,7 @@ This library could only exist thanks to the dedication of many volunteers around
     <tr>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/1nv"><img src="https://avatars.githubusercontent.com/u/10288828?v=4?s=100" width="100px;" alt="Eugene Selifonov"/><br /><sub><b>Eugene Selifonov</b></sub></a><br /><a href="https://github.com/PyFPDF/fpdf2/issues?q=author%3A1nv" title="Bug reports">🐛</a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://ez-startup.com"><img src="https://avatars.githubusercontent.com/u/69514175?v=4?s=100" width="100px;" alt="Kuth"/><br /><sub><b>Kuth</b></sub></a><br /><a href="#translation-kuth-chi" title="Translation">🌍</a></td>
-      <td align="center" valign="top" width="14.28%"><a href="https://rdbr.nl"><img src="https://avatars.githubusercontent.com/u/34062862?v=4?s=100" width="100px;" alt="Ruben de Bruin"/><br /><sub><b>Ruben de Bruin</b></sub></a><br /><a href="https://github.com/PyFPDF/fpdf2/commits?author=RubendeBruin" title="Code">💻</a></td>
+      <td align="center" valign="top" width="14.28%"><a href="https://rdbr.nl"><img src="https://avatars.githubusercontent.com/u/34062862?v=4?s=100" width="100px;" alt="Ruben de Bruin"/><br /><sub><b>Ruben de Bruin</b></sub></a><br /><a href="https://github.com/PyFPDF/fpdf2/commits?author=RubendeBruin" title="Code">💻</a> <a href="https://github.com/PyFPDF/fpdf2/commits?author=RubendeBruin" title="Documentation">📖</a></td>
     </tr>
   </tbody>
 </table>