add dream dataset
> Awesome good job !
> 
> Could you also add a dataset card using the template guide here : https://github.com/huggingface/datasets/blob/master/templates/README_guide.md
> If you can't fill some fields then just leave `[N/A]`

Quick amendment: `[N/A]` is for fields that are not relevant: if you can't find the information just leave `[More Information Needed]` @lhoestq since datset cards are optional for this sprint I'll add those later. Good for merge. Indeed we only require the tags to be added now (the yaml part at the top of the dataset card).
Could you add them please ?
You can find more infos here : https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md#tag-the-dataset-and-write-the-dataset-card @lhoestq added tags, I'll fill rest of the info after current sprint :) The tests are failing tests for other datasets, not this one. @lhoestq  could you tell me why these tests are failing, they don't seem related to this PR. 
Adding Dream: a Dataset and for Dialogue-Based Reading Comprehension

More details:
https://dataset.org/dream/
https://github.com/nlpdata/dream