Refactor directory structure

What we need is something similar to:

packaging_tutorial/
├── LICENSE
├── pyproject.toml
├── README.md
├── src/
│   └── example_package_YOUR_USERNAME_HERE/
│       ├── __init__.py
│       └── example.py
└── tests/




Currently we are missing the `example_package_YOUR_USERNAME_HERE/` layer