Adopt a Code of Conduct

[RangerMauve]

https://www.contributor-covenant.org/ looks good.

It'd be nice to add the markdown version to the repo and link to it in the README.

I'd really appreciate it if someone had a few spare minutes to add it in. 😁

Also down to look at other CoC templates if folks have alternatives they like more.

[humbletim]

here is another cc-sa template to consider:

https://github.com/processing/p5.js/blob/main/CODE_OF_CONDUCT.md

... not as exhaustive as contributor-covenant, but i really like how accessible the p5js versions feels -- and they way it captures into bullet points a collective mindset (ie: "we the community...") followed by actionable, individual responsibilities (ie: "be (mindful of self and community by)...").

[RangerMauve]

The p5 one looks cool too. Feel free to open a PR and we can get feedback from folks there. 😁