update readme to clarify async flag
update readme to clarify async flag

kedashoe/jake,cesarmarinhorj/jake,vinodpanicker/jake,kedashoe/jake,cesarmarinhorj/jake,jakejs/jake,talves/jake,kedashoe/jake,talves/jake,vinodpanicker/jake,jakejs/jake,cesarmarinhorj/jake,vinodpanicker/jake,talves/jake