Add instructions for Cygwin/X (alternative to Vcxsrv) as X Server

[Daniel Hubmann]

From #3 (comment).

The shortcut on the desktop needs to be like this:

C:\cygwin\bin\run.exe --quote /usr/bin/bash.exe -l -c "XWin :0 -listen tcp -retro -lesspointer -multiwindow -clipboard -wgl"

WSL2 needs the -ac flag to disable access control. See WSL2 issue or this with cygwin/x
https://gojimmypi.blogspot.com/2019/01/wsl-gui-using-cygwin-x-server-for.html