iio : Add ABI documentation for thresh falling/rising value in accel

This patch adds ABI documentation entries for
in_accel_thresh_falling_value, and in_accel_thresh_rising_value in /events.
There is at least one user for these, lis3l02dq in accel.
Signed-off-by: NHaneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -613,6 +613,8 @@ Description:
 		a given event type is enabled a future point (and not those for
 		whatever event was previously enabled).
 
+What:		/sys/.../events/in_accel_thresh_rising_value
+What:		/sys/.../events/in_accel_thresh_falling_value
 What:		/sys/.../events/in_accel_x_raw_thresh_rising_value
 What:		/sys/.../events/in_accel_x_raw_thresh_falling_value
 What:		/sys/.../events/in_accel_y_raw_thresh_rising_value