Add initial vignettes section

[Aariq]

I like this idea! One thing to keep in mind is the current setup with GitHub actions does not install R or Python and therefore cannot deal with code that needs to be run. If folks want to include interactive code chunks in vignettes, they'll have to render locally with quarto render and commit everything in _freeze/ before pushing to GitHub.

[KristinaRiemer]

I'll add a "How to add a vignette" section to the overview with that info! Thanks @Aariq.

[Aariq]

I'll add a "How to add a vignette" section to the overview with that info! Thanks @Aariq.

On second thought, there should probably be a generic "Editing This Book" section that all this can go in. I can take a crack at that if you'd like, then we can just cross-reference it here. I'm going to need to write a chapter like this for the lab handbook workshop anyways.