Clarify model documentation for `"gee"` and modes in general

[juliasilge]

There are a couple of outstanding issues from #631 that are only about clarifying wording.

Adjust how we talk about the "gee" engine

Replace this:

gee() always prints out warnings and output even when silent = TRUE. When using the gee engine, it will never produce output, even if silent = FALSE.

with this:

The gee::gee() function always prints out warnings and output even when silent = TRUE. The parsnip "gee" engine, by contrast, silences all console output coming from gee::gee(), even if silent = FALSE.

We could make this a template to avoid future mishaps.

Explain about extension packages

This code:

parsnip/man/rmd/aaa.Rmd

Lines 133 to 136 in 1439173

	ifelse(num_ext > 1,
	"There are parsnip extension packages ",
	"There is a parsnip extension package ")
	res <- paste0(x, "required to fit this model to this mode: ", res, ".")

generates sentences that end up being a bit confusing about mode:

There is a parsnip extension package required to fit this model to this mode: discrim.

When there is more than one, it sounds like they are all required to do any fitting, and it really looks like discrim is the mode. What about something different, like maybe:

There is a parsnip extension package required to fit this model configuration: discrim.

Maybe we don't need to mention mode right here?

There is a parsnip extension package required to fit this model: discrim.

[github-actions]

This issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with a reprex: https://reprex.tidyverse.org) and link to this issue.