Add all-contributors bot to OpenML repositories

[HeidiSeibold]

We'd love to acknowledge all our contributors. 👏

One way to do that is using a bot
https://github.com/all-contributors/all-contributors-bot

Would be great if someone would set it up for this repo and potentially other repos in the OpenML organization. 🎉

Please comment below if you have any questions or need clarification on this issue.

[prabhant]

Hi @HeidiSeibold.
I installed this bot for https://github.com/openml/blog repository. This works as intended.
I have installed this for OpenML and Openml.org repository too.

[HeidiSeibold]

Cool thanks @prabhant 👏

[HeidiSeibold]

Maybe someone would be interested in adding all the contributors to the READMEs in the respective repositories (for now openml/OpenML, openml/blog, openml/Openml.org, but potentially in all repos).

I think this would be nice. Should look like this in the end

(see https://github.com/all-contributors/all-contributors-bot/blob/master/README.md)