doc native: Clarify that in Windows one needs a VM for native_sim

Be more explicit about the need for a Virtual Machine running Linux if
running in Windows.
Also WSL2 has been out for ~5 years. Let's reduce the amount of info
on how  to run it in WSL1, as probably almost nobody is using it
anymore.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>