Add ArXiv paper URL

Add ArXiv paper URL.

README.md

@@ -167,7 +167,7 @@ Each instance contains a source sentence and four corrections. For example:
 This work is licensed under a [Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License](https://creativecommons.org/licenses/by-nc-sa/4.0/).
 
 ### Citation Information
-This benchmark was proposed by [Napoles et al., 2020](https://www.aclweb.org/anthology/E17-2037/).
+This benchmark was proposed by [Napoles et al., 2020](https://arxiv.org/abs/1702.04066).
 
 ```
 @InProceedings{napoles-sakaguchi-tetreault:2017:EACLshort,