Create a CONTRIBUTING file to help newcomers contribute to this project

[johnmartel]

This project uses a different set of tools than other projects at Valian, so it would be nice to have some context to those choices and how to quickly get going: what are important npm scripts, how to update dependencies, standards used, etc.

See: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/setting-guidelines-for-repository-contributors
See: https://contributing.md/how-to-build-contributing-md/
See: https://mozillascience.github.io/working-open-workshop/contributing/