Add an overview of ad insertion
Add an overview of ad insertion

PiperOrigin-RevId: 294689274

androidx/media,amzn/exoplayer-amazon-port,google/ExoPlayer,stari4ek/ExoPlayer,google/ExoPlayer,androidx/media,amzn/exoplayer-amazon-port,stari4ek/ExoPlayer,ened/ExoPlayer,stari4ek/ExoPlayer,ened/ExoPlayer,google/ExoPlayer,amzn/exoplayer-amazon-port,androidx/media,ened/ExoPlayer