Improve the help text for CONFIG_HWMON to let the users know how they
pick the right hardware monitoring driver(s) for their system.

Also fix a couple typos in the related documentation file and improve
some parts a bit.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>