Add WIT Dataset
@hassiahk is working on it  #2810  WikiMedia is now hosting the pixel values directly which should make it a lot easier!
The files can be found here:
https://techblog.wikimedia.org/2021/09/09/the-wikipedia-image-caption-matching-challenge-and-a-huge-release-of-image-data-for-research/
https://analytics.wikimedia.org/published/datasets/one-off/caption_competition/training/image_pixels/ > @hassiahk is working on it #2810

Thank you @bhavitvyamalik! Added this issue so we could track progress 😄 . Just linked the PR as well for visibility.  Hey folks, we are now hosting the merged pixel values + embeddings + metadata ourselves. I gave it a try - [nateraw/wit](https://huggingface.co/datasets/nateraw/wit)

**⚠️ - Make sure you add `streaming=True` unless you're prepared to download 400GB of data!**

```python
from datasets import load_dataset

ds = load_dataset('nateraw/wit', streaming=True)
example = next(iter(ds))
```

```python
>>> example = next(iter(ds['train']))
>>> example.keys()
dict_keys(['b64_bytes', 'original_width', 'image_url', 'wit_features', 'original_height', 'metadata_url', 'mime_type', 'caption_attribution_description', 'embedding'])
>>> example['wit_features'].keys()
dict_keys(['hierarchical_section_title', 'language', 'attribution_passes_lang_id', 'context_section_description', 'is_main_image', 'page_title', 'caption_title_and_reference_description', 'caption_alt_text_description', 'caption_reference_description', 'page_url', 'context_page_description', 'section_title', 'page_changed_recently'])
```
## Adding a Dataset
- **Name:** *WIT*
- **Description:** *Wikipedia-based Image Text Dataset*
- **Paper:** *[WIT: Wikipedia-based Image Text Dataset for Multimodal Multilingual Machine Learning
](https://arxiv.org/abs/2103.01913)*
- **Data:** *https://github.com/google-research-datasets/wit*
- **Motivation:**  (excerpt from their Github README.md)

> - The largest multimodal dataset (publicly available at the time of this writing) by the number of image-text examples.
> - A massively multilingual dataset (first of its kind) with coverage for over 100+ languages.
> - A collection of diverse set of concepts and real world entities.
> - Brings forth challenging real-world test sets.

Instructions to add a new dataset can be found [here](https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md).
