Document special On/Off key functions, and point at the information.

src/etc/etc.zaurus/sysctl.conf

@@ -1,3 +1,3 @@
 #machdep.allowaperture=2	# See xf86(4)
 #machdep.apmwarn=10		# battery % when apm status messages enabled
-#machdep.kbdreset=1		# permit console keyboard to do a nice halt
+#machdep.kbdreset=1		# permit zkbd(4) power key to do a nice halt