Adding license information for Openbookcorpus

[meg-huggingface]

Not entirely sure, following the links here, but it seems the relevant license is at https://github.com/soskek/bookcorpus/blob/master/LICENSE

[lhoestq]

The MIT license seems to be for the crawling code, no ? Then maybe we can also redirect users to the terms of smashwords.com regarding copyrights, in particular the paragraph 10 for end-users. In particular it seems that end users can download and use the content "for their personal enjoyment in any reasonable non-commercial manner in compliance with copyright law" and the smashwords end-users agreement.

It should be the same for #3526 as well

[severo]

Thanks, @meg-huggingface for the updates!

Thanks also for setting me as a reviewer, but I'm totally not a specialist of the datasets themselves, so I prefer to just lurk and let @lhoestq @albertvillanova @mariosasko or @patrickvonplaten review these changes.

[lhoestq]

May I merge this one ?

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.