Checklist before submitting an issue

• I have checked the existing issues and couldn't find an issue about this bug.

Issue details

• project_setup.md
  • Lots of unnecessary whitespace/newlines
  • "Package version number"
    • The package version is not in a single place (pyproject.toml), it is also present in src/test_package/__init__.py Is this both bumped? Needs quick testing.
  • MANIFEST.in and NOTICE could use more context, what is it good for?

_Originally posted by @OleMussmann in #554