Create CODE_OF_CONDUCT.md

[slayoo]

@nriemer @zdaq12 @jcurtis2
We've received feedback to our pyOpenSci sumbissiion: pyOpenSci/software-submission#179 (comment)
One of the comments relates to lack of a code of conduct statement for the project.
This PR includes a draft of it (based on the recently written numba-mpi CoC: https://github.com/numba-mpi/numba-mpi/blob/main/CODE_OF_CONDUCT.md) in which I've mentioned all our names as points of contact.
Please provide feedback, or it it seems OK and enough, please confirm your consent by approving this PR, thanks.

[github-actions]

CLANG WARNINGS:

error: no input files [clang-diagnostic-error]
error: no such file or directory: '/github/workspace/files/*.cpp' [clang-diagnostic-error]
error: unable to handle compilation, expected exactly one compiler job in '' [clang-diagnostic-error]

CPPCHECK WARNINGS:

CODE_OF_CONDUCT.md:21:16: error: No pair for character ('). Can't process file. File is either invalid or unicode, which is currently not supported. [syntaxError]
  collaborators' consent);
               ^
clang-tidy-report.txt:3:101: error: syntax error [syntaxError]
error: unable to handle compilation, expected exactly one compiler job in '' [clang-diagnostic-error]
                                                                                                    ^
nofile:0:0: information: Active checkers: There was critical errors (use --checkers-report=<filename> to see details) [checkersReport]

[nriemer]

Looks good to me! Thank you Sylwester!

[slayoo]

Thanks!