Add CovidQA dataset
It seems to share the same name as this dataset: https://openreview.net/forum?id=JENSKEEzsoU > It seems to share the same name as this dataset: https://openreview.net/forum?id=JENSKEEzsoU

you're right it can be confusing. I'll add the organization/research group for clarity: `covid_qa_castorini`. I added the dataset you shared as `covid_qa_deepset` in another PR (#1182)  Thanks for avoiding the name collision !
This PR adds CovidQA, a question answering dataset specifically designed for COVID-19, built by hand from knowledge gathered from Kaggle’s COVID-19 Open Research Dataset Challenge.

Link to the paper: https://arxiv.org/pdf/2004.11339.pdf
Link to the homepage: https://covidqa.ai