Add a code of conduct

[hollsk]

The Contributor Covenant is used by over 40,000 open source projects (including Pa11y!)

http://contributor-covenant.org/

[hollsk]

I've avoided doing this for months just because of one thing - we need a point of contact for people to privately raise issues (e.g. harassment, abuse, other violations).

I don't want that point of contact to be me, personally, and I don't think it would be appropriate if it were. The point of contact should be wholly neutral, to avoid situations where people have to report a violation to the individual who actually committed the violation.

Ideally, the POC would be a committee, not an individual. It would also help to state very clearly who the members of the committee are, so people know who they'd be submitting the report to. (see the approach khmer took: https://opensource.guide/code-of-conduct/#deciding-how-youll-enforce-your-code-of-conduct )

To date, only one person outside the company has collaborated with us, so this hasn't really been high on my list of things to do 😁

Jude, Danyal has assigned this to you for a decision.

[jpw]

This is still being worked-on -- turns out it's not easy!

But we are hopefully in the closing stages of getting this resolved.