Example config incomplete on which settings need gamemode group

[jn64]

gamemode.ini currently only mentions the gamemode group on renice and park_cores.

But from what I can tell, it is also required for disable_splitlock (via procsysctl), and probably a few other settings (which I'm not familiar with).

---

Instead of repeating the lines on each setting:

; To use this feature, the user must be added to the gamemode group (and then rebooted):
; sudo usermod -aG gamemode $(whoami)

I'd cut it down to:

; User must be in gamemode group.

and write the longer instructions once at the top of the file.