Add explanation on Python package installation process

[mcdonnnj]

💡 Summary

We should add to the development guide an explanation for why for Python package installation steps we typically lead with

python -m pip install --upgrade pip setuptools wheel

before installing other packages.

Motivation and context

We perform this step in most of our processes because of the need to upgrade pip and have wheel available. However, there is no explanation anywhere for why this is the case. We should document this here so that we have the rationale for this "on the record".

Implementation notes

Suitably explain why we upgrade pip and why we ensure setuptools and wheel are installed before proceeding with installing the Python packages actually required.

Acceptance criteria

• [ ] An approved pull request adding such documentation is approved and merged.

Original conversation

Is there a reason we can't/shouldn't consolidate this into a single line?

          python -m pip install --upgrade build pip setuptools wheel

Originally posted by @dav3r in https://github.com/cisagov/skeleton-python-library/pull/95#discussion_r826077269