Add KLUE dataset
I'm not sure why I got error like below when I auto-generate dummy data "mrc" 
```
datasets.keyhash.DuplicatedKeysError: FAILURE TO GENERATE DATASET !
Found duplicate Key: 0
Keys should be unique and deterministic in nature
``` > I'm not sure why I got error like below when I auto-generate dummy data "mrc"
> 
> ```
> datasets.keyhash.DuplicatedKeysError: FAILURE TO GENERATE DATASET !
> Found duplicate Key: 0
> Keys should be unique and deterministic in nature
> ```

Please check out the suggestion below. I think it might be a cause. > > I'm not sure why I got error like below when I auto-generate dummy data "mrc"
> > ```
> > datasets.keyhash.DuplicatedKeysError: FAILURE TO GENERATE DATASET !
> > Found duplicate Key: 0
> > Keys should be unique and deterministic in nature
> > ```
> 
> Please check out the suggestion below. I think it might be a cause.

The problem was `id_` in mrc when yield was not unique. (I used index in `enumerate(paragraphs)` by mistake)
I fixed it and update all the things To fix the CI you can just merge master into your branch and it should be all green hopefully :) @lhoestq
Thanks for reviewing!

It's harder than I thought to add dataset card. 😅 
I checked and updated your suggestion (script, readme details, dummy data). 

dummy data is little bit larger than expected because `ner` dataset is about 80 lines and `dp` dataset is about 25 lines to avoid 0 examples.

I'm not sure why some CI keep fails, can u check for this? Thanks ! That makes sense for ner and dp

For mrc on the other hand there are still too many examples, maybe you can generate the dummy data for 5 examples for all tasks except ner and dp ? > Thanks ! That makes sense for ner and dp
> 
> For mrc on the other hand there are still too many examples, maybe you can generate the dummy data for 5 examples for all tasks except ner and dp ?

Yes, I generate default lines in dataset-cli for other dataset except "dp" and "ner"
I fixed mrc dataset, hope it's fine now :)

the reason CI failed was I forgot to merge master into my branch 😅 
Add `KLUE (Korean Language Understanding Evaluation)` dataset released recently from [paper](https://arxiv.org/abs/2105.09680), [github](https://github.com/KLUE-benchmark/KLUE) and [webpage](https://klue-benchmark.com/tasks).
Please let me know if there's anything missing in the code or README.
Thanks!


