Added location to save scripts for cmdline programs

[MichaelBAnderson]

Included the required information for where to save R scripts for command-line programming. Originally it simply said to save the files (without detailing where to save the files). This took me quiet a while to figure this out while preparing for demonstration so I hope it helps others.

[HaoZeke]

Hi @MichaelBAnderson, thanks for this. I will merge this after setting alternate instructions for the linux and mac users, and I will also have to check that there is no specific format followed for operating specific instructions. Thank you for taking the time to contribute and I will get back to you on this if other changes are required in a bit.

[zkamvar]

I'm helping the current lesson Maintainers process outstanding pull requests on this repository, in preparation for transition to the new lesson infrastructure.

Thank you for this contribution @MichaelBAnderson. I appreciate you providing a location to save the R script based on your experience, but I am afraid that this recommendation (saving scripts in the same directory as the R executable) is not good practice because the scripts may not be portable. Instead, it would be better for users to use RStudio or add R to their PATH. Because of this, I will be closing this PR without merging the change. I'm sorry for the delay in reviewing your contribution and hope that you will continue to contribute to The Carpentries lessons.