Update readme to reflect changes in clean css -- causing breaking changes in current options API
Update readme to reflect changes in clean css -- causing breaking changes
in current options API

Closes #58

keremciu/gulp-minify-css,HaNdTriX/gulp-minify-css,MichaelFBA/gulp-minify-css,LoicMahieu/gulp-minify-css,mpath-development/gulp-minify-css,zarko-tg/gulp-minify-css,sibrus/gulp-minify-css