[arch-general] Incorporate udev rules in initrd

Hey guys, I set the sensitivity of my Thinkpad X230i laptop trackpoint with an udev rule setting the values in sysfs fitting for me. One drawback of this solution is that this rule I wrote is not incorporated inside of the intird, so when I start up, the udev of initrd already recognized the trackpoint and my rule in the booted-up system is ignored. My workaround for this is to manually do "udevadm trigger", which bugs the hell out of me. How can I tell mkinitcpio to include a custom udev rule? Do I need to write a hook for that? How can a hook for this look like? Thanks in advance! Christoph