x11-wm/picom: suggest mac_priority(4) after b22b6eeffd22
FreeBSD lacks setcap(8) + CAP_SYS_NICE, so permissions to set realtime
priorities like SCHED_RR are group-wide and disabled by default.
$ picom --log-level info
[...]
[ 20/01/2024 19:37:18.928 set_rr_scheduling INFO ] Failed to set real-time scheduling priority to 0. Consider giving picom the CAP_SYS_NICE capability
[...]