Document the use of wrap_* functions #338
Description
Mainly as a reminder, but it could be relevant to better document how to use wrap() and similar with ggduo() and ggpairs().
It could be through the evolution of existing vignettes. For example, for ggduo(), it could be better to start the vignette with basic examples, indicating to the users how to use ggduo() with the existing ggally_* functions before presenting advanced examples with custom functions.