Unvendor the `vignettes/` directory for R packages (#6160)
Unvendor the `vignettes/` directory for R packages (#6160)

Unvendor the vignettes directory for R packages

Co-authored-by: Colin Seymour <342564bc1ab1e55103f85104b5e013adfdf828cb@github.com>
github/linguist,github/linguist,github/linguist,github/linguist