Start & Maintain a guide on authoring & maintaining packages

# Background

In order to help people author and maintain high quality packages.

This can include things like
- CI best practices
- https://hexdocs.pm/mix_audit/2.1.5/readme.html (Erlang support?)
- Code best practices
- Dockerfile

This should be a single guide for as many beam languages as possible.

# Tasks

- [ ] Identify what should be in the guide
- [ ] Identify an MVP set of improvements
- [ ] Identify weak spots in various tooling