Provide doc topic for <tidy-select>

[hadley]

e.g.

#' Argument type: tidy-select
#'
#' @description
#' This page describes the `<tidy-select>` argument modifier which
#' indicates that the argument uses **tidy selection**, a sub-type of
#' tidy evaluation. If you've never heard of tidy evaluation before,
#' start by reading
#' <https://r4ds.hadley.nz/functions.html#data-frame-functions>.
#'
#' # Overview of selection features
#'
#' ```{r, child = "man/rmd/overview.Rmd"}
#' ```
#'
#' # Indirection
#'
#' There are two main cases:
#'
#' *   If you have a character vector of column names, use `all_of()`
#'     or `any_of()`, depending on whether or not you want unknown variable
#'     names to cause an error, e.g `unnest(df, all_of(vars))`,
#'     `unnest(df, !any_of(vars))`.
#'
#' *   If you want the user to supply a tidyselect specification in a
#'     function argument, you need to tunnel the selection through the function
#'     argument. This is done by embracing the function argument `{{ }}`,
#'     e.g `unnest(df, {{ vars }})`.
#'
#' Learn more in `vignette("programming.Rmd")`.
#'
#' @keywords internal
#' @name tidyr_tidy_select
NULL

[DavisVaughan]

We could definitely use this in yardstick too for truth, estimate, and ... arguments

And workflows with add_variables()