README: Add "udevcontrol reload_rules" to postinst
README: Add "udevcontrol reload_rules" to postinst

- The POST-INSTALLATION section did not mention the need to reload the
udev rules.  Fix this.

- Improve ordering of postinst instructions

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr