Add CRAN cookbook to release_checklist()

I recently developed a new package and followed the `usethis::release_checklist()` yet still got some comments from CRAN and they pointed me to https://contributor.r-project.org/cran-cookbook

So, I think it would useful to add [the ](https://contributor.r-project.org/cran-cookbook) to `usethis::release_checklist()`, possibly above `todo("Review <https://github.com/DavisVaughan/extrachecks>")`.