Add SubjQA dataset
Hello datasetters 🙂!

Here's an interesting dataset about extractive question-answering on _subjective_ product / restaurant reviews. It's quite challenging for models fine-tuned on SQuAD and provides a nice example of domain adaptation (i.e. fine-tuning a SQuAD model on this domain gives better performance).

I found a bug in the start/end indices that I've proposed a fix for here: https://github.com/megagonlabs/SubjQA/pull/2

Unfortunately, the dataset creators are unresponsive, so for now I am using my fork as the source. Will update the URL if/when the creators respond.
I'm not sure why the windows test fails, but looking at the logs it looks like some caching issue on one of the metrics ... maybe re-run and 🤞 ? Hi @lewtun, thanks for adding this dataset!

If the dataset is going to be referenced heavily, I think it's worth spending some time to make the dataset card really great :) To start, the information that is currently in the `Data collection` paragraph should probably be organized in the `Dataset Creation` section.

Here's a link to the [relevant section of the guide](https://github.com/huggingface/datasets/blob/master/templates/README_guide.md#dataset-creation), let me know if you have any questions! > If the dataset is going to be referenced heavily, I think it's worth spending some time to make the dataset card really great :) To start, the information that is currently in the `Data collection` paragraph should probably be organized in the `Dataset Creation` section.

great idea @yjernite! i've added some extra information / moved things as you suggest and will wrap up the rest tomorrow :) hi @yjernite and @lhoestq, i've fleshed out the dataset card and think this is now ready for another round of review!