Added tax specifications to README file
CS

Just coding style + whitespaces removed
Added new settings to store config

1. Enable "germanization" using a checkbox. Hide all options if not enabled
2. Define which member groups have net prices
Added new tax class configuration

In a germanized store, we do not need tax rates. A tax class defines
if it has net or gross prices, and what german tax to apply.
You can create multiple tax classes for different products
(e.g., some with 19% tax and some with 7%)
Added multiple helper methods to determine the current customer situation
Generate tax notice based on current customer situation
Calculate german taxes

If germanization is enabled, overwrite the default tax calculation
functionality. We then calculate only german taxes based on tax class
configuration.