iio: Add ABI documentation for offset and scaled humidity

This patch adds ABI documentation entries for in_humidityrelative_offset
and in_humidityrelative_scale, since there is at least one user for these,
Si7005 humidity and temperature sensor driver.
Signed-off-by: NRoberta Dobrescu <roberta.dobrescu@gmail.com>
Reviewed-by: NDaniel Baluta <daniel.baluta@intel.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -238,6 +238,7 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_tempY_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_temp_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressureY_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressure_offset
+What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_offset
 KernelVersion:	2.6.35
 Contact:	linux-iio@vger.kernel.org
 Description:
@@ -273,6 +274,7 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_rot_from_north_magnetic_tilt_comp_sca
 What:		/sys/bus/iio/devices/iio:deviceX/in_rot_from_north_true_tilt_comp_scale
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressureY_scale
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressure_scale
+What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_scale
 KernelVersion:	2.6.35
 Contact:	linux-iio@vger.kernel.org
 Description: