media: vivid.rst: describe display present control

Signed-off-by: Johan Korsnes <johan.korsnes@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/v4l-drivers/vivid.rst

@@ -941,6 +941,11 @@ Digital Video Controls
 	affects the reported colorspace since DVI_D outputs will always use
 	sRGB.
 
+- Display Present:
+
+	sets the presence of a "display" on the HDMI output. This affects
+	the tx_edid_present, tx_hotplug and tx_rxsense controls.
+
 
 FM Radio Receiver Controls
 ~~~~~~~~~~~~~~~~~~~~~~~~~~