Thoughts on the "Add some dependencies" challenge

I'm referring to: https://github.com/carpentries-incubator/lesson-R-packaging/blob/965117c6127396e112c70dae30ff2760bc75b49c/episodes/dependencies.Rmd#L67

I'm worried that:
* We're introducing a challenge without having actually given the users the tools to solve the challenge. Namely, they haven't learned about `usethis::use_package()` yet. Shouldn't we do this before testing them on it?
* Neither `knitr` nor `tidyr` are actually used in the package. Also, it's a bit odd that `knitr` is the mandatory dependency and `tidyr` the optional one, given that `knitr` is almost always a `Suggests` dependency. Could this example be changed to something that makes sense in the overall narrative of the package being built here?

Start at episodes/dependencies.Rmd around line 67 and read the surrounding lesson narrative and challenge. Check whether learners have been introduced to usethis::use_package(), then revise the example so the dependencies are used in the package and their mandatory or optional roles fit the lesson.】【。

Written by the indexing model from the issue text.