Expand file structure step in Create_a_python_package.ipynb

The file structure step in Create_a_python_package.ipynb could be expanded. First, it would be useful to actually typeset the file structure instead of using bullets, such as in the following:

├── package │ ├── init.py │ └── other_script.py └── setup.py

This would be particularly useful since the linked example doesn't conform to the stated structure (it doesn't include setup.py).

Furthermore, it would be useful to note that there are two major ways of approaching this: a flat layout and a src layout. See this link for descriptions of this: https://medium.com/mlearning-ai/a-practical-guide-to-python-project-structure-and-packaging-90c7f7a04f95