Adding new lesson to R Programming about workspace and files

I have created a new lesson for R Programming about workspaces and files. Are you interested in contributions like this? If so, I have lots of more material, left over from a class I taught 5 years ago. This material is not really worth a new course, but it would fit nicely as additional lessons in R Programming. But, before I add it all, I thought that I would seek your feedback. (I am experienced with R but very new to Github, so apologies if this pull request is not the best way to suggest this change.)