media: Documentation: vidtv: Add ReST documentation for vidtv

Add documentation for the Virtual Digital TV driver (vidtv) in the
Restructured Text (ReST) format.

This discusses:
- What is vidtv
- Why vidtv is needed
- How to build and run vidtv
- How vidtv is structured
- How to test vidtv
- How to improve vidtv

[mchehab: fixed bad whitespaces]
Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/media/drivers/index.rst

@@ -35,4 +35,5 @@ Digital TV drivers
 
 	dvb-usb
 	frontends
+	vidtv
 	contributors