Adding OneStopEnglish corpus dataset
CONTRIBUTOR
Hi @lhoestq, thanks for the review.
I have made all the changes, PTAL! :) 
2020-12-08T18:30:19Z
https://github.com/huggingface/datasets/pull/1269#issuecomment-740823764
https://api.github.com/repos/huggingface/datasets/issues/1269
MDEyOklzc3VlQ29tbWVudDc0MDgyMzc2NA==
https://api.github.com/repos/huggingface/datasets/issues/comments/740823764/reactions
2020-12-08T18:30:19Z
https://api.github.com/repos/huggingface/datasets/issues/comments/740823764
https://avatars.githubusercontent.com/u/22298787?v=4
https://api.github.com/users/purvimisal/events{/privacy}
https://api.github.com/users/purvimisal/followers
https://api.github.com/users/purvimisal/following{/other_user}
https://api.github.com/users/purvimisal/gists{/gist_id}
https://github.com/purvimisal
purvimisal
MDQ6VXNlcjIyMjk4Nzg3
https://api.github.com/users/purvimisal/orgs
https://api.github.com/users/purvimisal/received_events
https://api.github.com/users/purvimisal/repos
https://api.github.com/users/purvimisal/starred{/owner}{/repo}
https://api.github.com/users/purvimisal/subscriptions
User
https://api.github.com/users/purvimisal
public
This PR adds OneStopEnglish Corpus containing texts classified into reading levels (elementary, intermediate, advance) for automatic readability assessment and text simplification. 

Link to the paper: https://www.aclweb.org/anthology/W18-0535.pdf 