DOC: Add CoC to the README
- [ ] closes # xxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@sparalic can you merge master & repush? Looks like there was an unrelated CI failure. @datapythonista I explicitly pushed the file I updated, and did a `git diff upstream/master` to confirm the changes. Is that wrong? Judging on below it seem as if I made it worse. Not sure what was the problem. You can have a look at the [Files changed](https://github.com/pandas-dev/pandas/pull/27780/files) tab, and you'll see that there are 4 files that are unrelated to what you're changing, and that we don't want to merge into the repo.

Also, I think you reverted some of the changes you already made from a review. We will check later what went wrong, for now you can delete the files in your branch, and leave exactly what you want to get merged in pandas, and then push the branch again. @sparalic : FYI, if you're having issues pushing, we can definitely help you out instead of your closing the PR.