[FFmpeg-devel] [PATCH] Add FAQs about running in background

[Jim DeLaHunt]

Add FAQs about running in background

Add two FAQs about running FFmpeg in the background.
The first explains the use of the -nostdin option in
a straightforward way.

The second FAQ starts from a confusing error message,
and leads to the solution, use of the -nostdin option.
The purpose of the second FAQ is to attract web searches
from people having the problem, and offer them a solution.

Add an anchor to the Main Options section of the ffmpeg
documentation, so that the FAQs can link directly there.

This changes only two documentation files, no code. FATE passes.

(This is my first attempt to submit a patch. If I have done
it wrong, please help me fix it. Thanks! --Jim DeLaHunt)