add detailed step-by-step install guide for Windows per recommendation from SimSec

It was pointed out to us that many Windows users will not consider it obvious which Java they should be using and other aspects of the install process. We were advised to create a step-by-step help guide for installing I2P. One example of such a guide we were directed to was the set provided by Mullvad. This guide was created on a newly installed, completely unchanged Windows 10 system.