Update ffmpeg instructions in README
Update ffmpeg instructions in README

nerdzeu/NERDZCrush,nerdzeu/NERDZCrush,roderickm/MediaCrush,roderickm/MediaCrush,MediaCrush/MediaCrush,roderickm/MediaCrush,nerdzeu/NERDZCrush,MediaCrush/MediaCrush