[Python-Dev] Do not harass other mailing list subscribers privately

The SC has been notified of at least one instance of someone subscribed to this list harassing another subscriber privately. We wanted to remind folks that we expect people to behave reasonably towards each other, else people risk losing access to this mailing list and other places where Python is developed per the Code of Conduct. Poor behaviour, public or private, is not acceptable and will have ramifications where we are trying to facilitate an open, considerate, and respectful community that is under our control. -Brett, on behalf of the Python steering council