Add empty_date documentation to readme
Add empty_date documentation to readme

TuxmAL/simple_calendar,excid3/simple_calendar,timshingyu/simple_calendar,timshingyu/simple_calendar,excid3/simple_calendar,sdbeng/simple_calendar,TuxmAL/simple_calendar,rodrigoargumedo/simple_calendar,sdbeng/simple_calendar,rodrigoargumedo/simple_calendar,sdbeng/simple_calendar,rodrigoargumedo/simple_calendar,timshingyu/simple_calendar,excid3/simple_calendar