Better workflowr refererence

[athchen]

I think this link is a better starter/reference for workflowr. Not sure if the README is more updated than this but they should be mostly the same: https://jdblischak.github.io/workflowr/

https://github.com/jtleek/ads2020/blob/13eef18b2e8ed1f304a2ededceaf9b13976427b4/03-week.Rmd#L388