doc: iio: ad4695: document buffered read

Update the ad4695 documentation to say that buffered reads are
supported. Since there are 4 possible modes of reading conversion data,
it is useful to know which one is actually being used, namely the
advanced sequencer mode.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20240813-iio-adc-ad4695-buffered-read-v2-2-9bb19fc1924b@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/iio/ad4695.rst

@@ -147,9 +147,16 @@ Unimplemented features
 ----------------------
 
 - Additional wiring modes
-- Buffered reads
 - Threshold events
 - Oversampling
 - Gain/offset calibration
 - GPIO support
 - CRC support
+
+Device buffers
+==============
+
+This driver supports hardware triggered buffers. This uses the "advanced
+sequencer" feature of the chip to trigger a burst of conversions.
+
+Also see :doc:`iio_devbuf` for more general information.