Part 3 - install rtools

[mingyu-yuan]

We ran into the issue of installing rtools during the workshop today. (Jose & Mingyu)

Make a note in Part 3 (also possibly in the end of Part 2) that rtools need to be installed for PC users to install tidyverse properly.

It is worth mentioning this at the end of Part 2 to leave folks more time to figure this out so as to avoid spending time on this during Part 3.

[heroashman]

I've added a warning that if this happens the best thing is for people to switch to DataHub. RTools should have installed when people installed R and RStudio locally so I think it indicates a broader problem with their install taht we won't want to troubleshoot at the start of the workshop.