docs: media: mgb4: Improve mgb4 driver documentation

Add some basic info about the HW/driver + contact info.

Signed-off-by: Martin Tůma <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

Documentation/admin-guide/media/mgb4.rst

···
 .. SPDX-License-Identifier: GPL-2.0
 
+.. include:: <isonum.txt>
+
 The mgb4 driver
 ===============
+
+Copyright |copy| 2023 - 2025 Digiteq Automotive
+    author: Martin Tůma <[e-mail]>
+
+This is a v4l2 device driver for the Digiteq Automotive FrameGrabber 4, a PCIe
+card capable of capturing and generating FPD-Link III and GMSL2/3 video streams
+as used in the automotive industry.
 
 sysfs interface
 ---------------