Document release process

Maybe add the release process to CONTRIBUTING

```
Update changelog date
Bump package.json
commit -m '6.4.0'
git tag v6.4.0
git push ; git push --tags
npx gh-release
npm publish
```

Open CONTRIBUTING and compare its current release guidance with the release steps in the issue. Document the changelog update, package.json bump, commit and tag commands, pushes, gh-release invocation, and npm publish step; done means the process is recorded clearly in CONTRIBUTING.

Written by the indexing model from the issue text.