Reformat releasenotes.md
Reformat releasenotes.md

PiperOrigin-RevId: 305242260

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