Make it easier to discover and exploit the "tidyverse.quiet" option

[jennybc]

I recently needed to use this in the R Packages book and went to the tidyverse package's pkgdown site for a refresher. We should make it easier to discover this option.

In R code:

options(tidyverse.quiet = TRUE)

withr::local_options(tidyverse.quiet = TRUE)

In a code chunk:

```{r}
#| R.options = list(tidyverse.quiet = TRUE)
library(tidyverse)
```

```{r somechunk, R.options = list(tidyverse.quiet = TRUE)}
library(tidyverse)
```