contributing documentation overhaul

[jcgsville]

Description

Did an overhaul on Contributing docs to make them up-to-date with the latest changes and provide info on the things I had to figure out myself.

I also fixed the yarn website script, which was not working, and I added the yarn cli script. I'm not deeply opinionated about having yarn cli, so if you think it's not useful enough to add to package.json scripts, I'm happy to update it and update the docs.

Also, when I ran docker compose I got this warning, so I removed the version line as instructed.

WARN[0000] /path/to/graphile/worker/docker-compose.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avoid potential confusion 

Checklist

• My code matches the project's code style and yarn lint:fix passes.

[jcgsville]

Thanks for the additions and corrections, @benjie