Documentation: iio: Clarify meaning of IIO_DISTANCE channel type

IIO_DISTANCE is used for two purposes: for pedometers to record the
distance covered by a walker, and to measure the distance to an object

IIO_DISTANCE is in meters while IIO_PROXIMITY is a unitless measure
indirectly proportional to distance (higher value relates to a closer
object)
Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio

@@ -1242,9 +1242,9 @@ What:		/sys/.../iio:deviceX/in_distance_raw
 KernelVersion:	4.0
 Contact:	linux-iio@vger.kernel.org
 Description:
-		This attribute is used to read the distance covered by the user
-		since the last reboot while activated. Units after application
-		of scale are meters.
+		This attribute is used to read the measured distance to an object
+		or the distance covered by the user since the last reboot while
+		activated. Units after application of scale are meters.
 
 What:		/sys/bus/iio/devices/iio:deviceX/store_eeprom
 KernelVersion:	3.4.0