Consider changing helper `md` files to `Rmd`

[Stephanie Spielman]

I wonder if we should convert the following to Rmd -

• intro-to-R-tidyverse/00a-rstudio_guide.md
• intro-to-R-tidyverse/00b-debugging_resources.md
• intro-to-R-tidyverse/00c-good-scientific-coding-practices.md

Mostly wondering this because the first two documents (particularly the first one) have screenshots, and if the files were Rmd, the screenshots would have little inline previews! Otherwise you have to render the HTML, which trainees may not know to do. Might as well do all three if we're going to do one.

All that said, it's not clear to me how much our trainees actually use these documents, but an md -> Rmd conversion is at least pretty quick to do.