Add version-specific BibTeX
Maybe we should only keep one citation ?
cc @thomwolf @yjernite  For info:
- The one automatically generated by Zenodo is version-specific, and a new one will be generated after each release.
- Zenodo has also generated a project-specific DOI (they call it *Concept DOI* as opposed to *Version DOI*), but currently this only redirects to the DOI page of the latest version.
- All the information automatically generated by Zenodo can be corrected/customized if necessary.
  - If we decide to correct/update metadata, take into account that there are the following fields (among others): Authors, Contributors, Title, Description, Keywords, Additional Notes, License,...

According to Zenodo: https://help.zenodo.org/#versioning
> **Which DOI should I use in citations?**
> 
> You should normally always use the DOI for the specific version of your record in citations. This is to ensure that other researchers can access the exact research artefact you used for reproducibility. By default, Zenodo uses the specific version to generate citations.
> 
> You can use the Concept DOI representing all versions in citations when it is desirable to cite an evolving research artifact, without being specific about the version. Thanks for the details ! As zenodo says we should probably just show the versioned DOI. And we can remove the old citation. I have removed the old citation.

What about the new one? Should we customize it? I have fixed some author names (replaced nickname with first and family names). Note that the list of authors is created automatically by Zenodo from this list: https://github.com/huggingface/datasets/graphs/contributors
I do not know if this default automatic list of authors is what we want to show in the citation...
As pointed out by @lhoestq in #2411, after the creation of the Zenodo DOI for Datasets, a new BibTeX entry is created with each release.

This PR adds a version-specific BibTeX entry, besides the existing one which is generic for the project.

See version-specific BibTeX entry here: https://zenodo.org/record/4817769/export/hx#.YLSyd6j7RPY