Add docs about presentation transitions in README.md
Add docs about presentation transitions in README.md

denodster/viewer.js,denodster/viewer.js,box/viewer.js,lakenen/viewer.js,denodster/viewer.js,lakenen/viewer.js,lakenen/viewer.js,box/viewer.js,vdclouis/viewer.js,vdclouis/viewer.js,box/viewer.js,vdclouis/viewer.js