[R] tibble or data.frame?

The language is a bit loose in a few places. I'd suggest at least noting that `tibble` is not required, but that the data frames returned by arrow include the tibble class attributes. So if you use tibble, they'll print and otherwise behave like tibbles. Otherwise, they're just `data.frame`s and that's fine.

You may also want to consider have (at least) your first examples use `data.frame(...)` to make clear that tibble is not required. (This is a cookbook, and (food) recipes often allow for substitutions or tell you ways you can do variations on it, right?)

Start by reviewing the cookbook's R sections and the first examples that use data frames. Clarify that tibble is optional, explain the tibble class attributes returned by Arrow, and use data.frame(...) in initial examples where appropriate; the documentation should clearly distinguish the two choices.

Written by the indexing model from the issue text.