man: SYMLINK can be matched as well as assigned

man: SYMLINK can be matched as well as assigned

If by-path / by-id links don't quite do what you want, this is a nice
clean way to extend the behaviour.  Real example:

SYMLINK=="serial/by-id/usb-Novatel_Wireless_Inc*CDMA*-if00-port0", \\
 SYMLINK+="cellcard"

Some users ask how to do things like this.

 - create an additional link with a shorter name
 - create a link which matches more loosely
    (omit certain path segments e.g. serial numbers)
 - change permissions on certain USB device nodes

Allow them to realize this without reading the friendly *.c files.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>