Update CODE_OF_CONDUCT.md

[gniumg-source]

@suztomo #2620
@chingor13 #2619
@foxxtrot #2545
@hgschmie #2540
@anuraaga #1861

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• [ •] Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• [• ] Ensure the tests and linter pass
• [ •] Code coverage does not decrease (if any source code was changed)
• [ •] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the samples format.