Update README for building cut-down FFmpeg
Update README for building cut-down FFmpeg

macOS Sierra’s otool still prints the library header when using -X.

Newer versions of FFmpeg always link against CoreServices and
VideoDecodeAcceleration framework (all of which we don't want / need).
I haven’t found a way to avoid this other than editing `configure`.

q-p/SoundPusher,q-p/SoundPusher,q-p/SoundPusher