Add contributing information

[mfeurer]

@amueller a lot of this is actually copied from scikit-learn. Is there a special template that I need to follow to make this legally correct?

[codecov-io]

Codecov Report

Merging #368 into develop will increase coverage by 0.12%.
The diff coverage is n/a.

@@ Coverage Diff @@## develop #368 +/- ##
==========================================
+ Coverage 89.37% 89.5% +0.12% 
==========================================
Files 32 32 Lines 2683 2744 +61 ==========================================
+ Hits 2398 2456 +58 - Misses 285 288 +3

Impacted Files	Coverage Δ
openml/datasets/dataset.py	81.01% <0%> (+3.36%)	⬆️

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[mfeurer]

@amueller do you have some time to review this one? I think you're most experienced with user engagement.

[nok]

I prefer using the branch type as a suffix to keep the overview, i.e.: feature/idea or feature-idea.

[amueller]

sorry @mfeurer not looking at github notifications right now (have 20000+)
What do you mean by legally correct?

[nok]

Legally, because the content of these files are partially copied from the scikit-learn/scikit-learn repository (CONTRIBUTING.md, ISSUE_TEMPLATE.md, PULL_REQUEST_TEMPLATE.md) I guess.

[mfeurer]

Yep, those files are somewhat copied from scikit-learn, so to follow the BSD-license, we need to mention that. How about following this proposal?

[mfeurer]

Okay, I just added a note about the files in question and added the license of scikit-learn to our license file. Should be fine like this.

[PGijsbers]

I can't review anymore since I made the last change, right?

[PGijsbers]

Not an expert on the legality of it, but I seems fine to me. I made a change that mentions how to run unit tests for Windows users briefly.