Add info about BT.709 recommendation

[ismaelbej]

Now the majority of the videos are done in BT 709, which is used by HD television, a comparison with the standard for SD BT.601 should be good addition.

[guilt]

Do add BT.2020 as well :-)

https://en.wikipedia.org/wiki/Rec._2020

[guilt]

Would be helpful to expand the bandwidth section as well, talk about what practical HD video bandwidth looks like, esp. wrt HDMI: Resolution, Color space and FPS.