Add a code of conduct

[The-Compiler]

See #5709 and the mails linked from there. I added a list of people included in coc@pytest.org at the bottom.

[codecov]

Codecov Report

Merging #5711 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5711      +/-   ##
==========================================
- Coverage   96.17%   96.16%   -0.01%     
==========================================
  Files         117      117              
  Lines       25864    25864              
  Branches     2498     2498              
==========================================
- Hits        24875    24873       -2     
- Misses        689      690       +1     
- Partials      300      301       +1

Impacted Files	Coverage Δ
src/_pytest/pastebin.py	87.71% <0%> (-3.51%)	⬇️

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[nicoddemus]

Looks good!

I believe we should add this to the docs (so it needs to be converted to .rst), and link it from the README too to gain more visibility.

besides being on the docs, I think it deserves to appear on the side bar too:

Perhaps after "Contributing"?

[nicoddemus]

Please see my comment 👍

[The-Compiler]

Sounds good as long as GitHub still picks it up as well. @nicoddemus if you have the time, could you maybe pick this up? I'm quite busy with exams so I can't commit to continuing working on this until next month.

[asottile]

Content looks good! Thanks for this

[nicoddemus]

Hmmm oh right: https://help.github.com/en/articles/adding-a-code-of-conduct-to-your-project

It seems it only supports .md. Well in that case I suppose we can close this, as it will get enough visibility by GitHub's own means (issues and PRs).