[MNT] Add all-contributors

Author: xuyxu

CONTRIBUTORS.md

@@ -0,0 +1,10 @@
+Contributors
+============
+
+<table>
+  <tr>
+    <td align="center"><a href="https://github.com/xuyxu"><img src="https://avatars.githubusercontent.com/u/22359569?s=400&u=9bb18ef27fee8b561a7be585d3b96d74e0398eac&v=4" width="100px;" alt=""/><br /><sub><b>Yi-Xuan Xu</b></sub></a><br /><a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=xuyxu" title="Code">💻</a> <a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=xuyxu" title="Documentation">📖</a> <a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=xuyxu" title="Tests">⚠️</a></td>
+    <td align="center"><a href="https://github.com/zzzzwj"><img src="https://avatars.githubusercontent.com/u/23235538?s=400&v=4" width="100px;" alt=""/><br /><sub><b>Wen-Jie Zhang</b></sub></a><br /><a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=zzzzwj" title="Code">💻</a> <a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=zzzzwj" title="Tests">⚠️</a></td>
+    <td align="center"><a href="https://github.com/mttgdd"><img src="https://avatars.githubusercontent.com/u/3154919?s=400&u=3e6287b0c4a2c83e2db98d86980cee89ed218d32&v=4" width="100px;" alt=""/><br /><sub><b>Matt Gadd</b></sub></a><br /><a href="https://github.com/xuyxu/Ensemble-PyTorch/commits?author=mttgdd" title="Code">💻</a></td>
+  </tr>
+</table>