docs: iio: add ADXL313 accelerometer

Add documentation for the ADXL313 accelerometer driver.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250702230819.19353-9-l.rubusch@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>