add missing CelebA in docs

[edgarriba]

this PR add to docs the reference to CelebA dataset in torchvision.
code is here: https://github.com/pytorch/vision/blob/master/torchvision/datasets/celeba.py

but no reference for some reason

[fmassa]

Thanks Edgar!

[edgarriba]

@fmassa I observed a couple of things when trying to use this dataset. Hosting the data in gdrive completely blocks to use the dataset when the quota have exceed. This comes from authors website, not torchvision problem. However to make it more functional (from tv) would be great to provide an alternative or at least specify that in the docs offering alternative ways to use this dataset. In my case after spending some time trying to understand why I couldn't use it out of the box, I ended up downolading from other source and using ImageFolder.

[fmassa]

We won't be hosting the dataset ourselves (it's outside of the scope of torchvision). If downloading from Google Drive is the only official way, then I think this is the way we should move forward.

If there are other official sources with the dataset, then it would be worth considering.

[edgarriba]

gotcha, just making the point that giving good interfaces to some datasets in specific format but not assuring data accessibility could lead the API to be can of useless if I want to use it but I cannot access to the data. Talking after facing this issue in this specific dataset, don't have any other opinion for the others :)

we had similar discussions in kornia e.g. to host weights and stuff to assure that the user will always have a fully functional API.

[fmassa]

I understand. The download functionality is meant to be a helper to get started, but if the user can't access the data because the original dataset disappeared (as was the case with ImageNet for example #1457), we remove the download functionality and let the user download it by themselves (if at all possible).

From the README of torchvision https://github.com/pytorch/vision#disclaimer-on-datasets

This is a utility library that downloads and prepares public datasets. We do not host or distribute these datasets, vouch for their quality or fairness, or claim that you have license to use the dataset. It is your responsibility to determine whether you have permission to use the dataset under the dataset's license.

If you're a dataset owner and wish to update any part of it (description, citation, etc.), or do not want your dataset to be included in this library, please get in touch through a GitHub issue. Thanks for your contribution to the ML community!