hwmon: Update the sysfs interface documentation

* Document the characteristics of libsensors 3.0.0 and 3.0.1.
* The sysfs interface is no longer subject to changes.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Juerg Haefliger <juergh at gmail.com>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>