Proposal to add MedMCQA dataset

## Adding a Dataset
- **Name:** *MedMCQA : A Large-scale Multi-Subject Multi-Choice Dataset for Medical domain Question Answering*
- **Description:** *A large-scale (194k), Multiple-Choice Question Answering (MCQA) dataset designed to address real-world medical entrance exam questions.*
- **Task:** *QnA*
- **Paper:** *https://arxiv.org/abs/2203.14371*
- **Data:** *https://github.com/medmcqa/medmcqa*
- **License:** *[Apache-2.0 License](https://github.com/medmcqa/medmcqa/blob/main/LICENSE)*
- **Motivation:** *It is a very recent large-scale medical QA dataset, that covers ~20 different topics of entrance exam questions*