Update README.md for X11 and Wayland instructions

[derenv]

Expected Behavior

We should have clear instructions that work with both X11 and Wayland systems, as Nvidia+Wayland systems are slowly becoming more viable. This should reduce the potential for user confusion (and probably issues for us to respond to) in future.

for example, nvidia-settings is slowly getting working updates!

Current Behavior

The shortcut mentioned here only functions on X11 systems, though for Wayland the only way to reload is to logout and login again, so i think only a minor modification to say that explicitly should be needed.

[derenv]

results of #212 will probably require a README rewrite, so can try to fit this in there.

[kenohassler]

closed in #214