updated README with selection-related info
updated README with selection-related info

katspaugh/wavesurfer.js,ffxsam/wavesurfer.js,katspaugh/wavesurfer.js,ale-grosselle/wavesurfer.js,agamemnus/wavesurfer.js,ffxsam/wavesurfer.js,ale-grosselle/wavesurfer.js,agamemnus/wavesurfer.js