Remove mentioning Linux and MacOS in the README.md

[DeeDeeRanged]

This is a Windows only GUI so please remove any mention of Linux and MacOS as that makes things much clearer.

[DeeDeeRanged]

The following is still mentioned in the README.MD under System requirements:

WINDOWS XP,7,8,10 or later (x64) / LINUX / MAC OS

Please remove the mentioning of LINUX/MACOS as this is a Windows miner only.