Improved Quorum-Genesis Docs

[john-osullivan]

Two key improvements:

1. All of the script's functions now have docstrings, making the code is easier to understand from mouse-over glances.
2. The README now explains how EVM storage is built, as that's the core confusing part of the script.
3. Previous README content was updated to reflect how the config is actually consumed in our POW model.