iio: document linear acceleration modifiers

Introduce ABI documentation for new IIO modifiers used for reporting
"linear acceleration" measures.
Signed-off-by: Andrea Merello <andrea.merello@iit.it>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220907132205.28021-3-andrea.merello@iit.itSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio

@@ -260,6 +260,15 @@ Description:
 		Has all of the equivalent parameters as per voltageY. Units
 		after application of scale and offset are m/s^2.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_linear_x_raw
+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_linear_y_raw
+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_linear_z_raw
+KernelVersion:	6.1
+Contact:	linux-iio@vger.kernel.org
+Description:
+		As per in_accel_X_raw attributes, but minus the
+		acceleration due to gravity.
+
 What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_x_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_y_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_z_raw