doc/user: update the udev rule to handle bind/unbind events

doc/user: update the udev rule to handle bind/unbind events

Summary: we expect add, change or remove but kernel 4.12 added bind and
unbind. These events were previously discarded by udevd. Our rules should
handle any event *but* remove, so update as suggested in the announce email
linked below.

For a longer explanation, see the system 247rc2 announcement
https://lists.freedesktop.org/archives/systemd-devel/2020-November/045570.ht

See cd37dcfa66d59ecbdf787ee1aa34bb65f2a38b6d where we did this already
for the udev rules we use ourselves.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>