Suggestion: cite the r-ci-samples repo as well

[MichaelChirico]

https://github.com/r-lib/pkgdown/blob/676cf1dce39e4dc5aa1bcb671b1e14e992589a0a/vignettes/how-to-update-released-site.Rmd#L290

_pkgdown.yml is one of the files I track in the r-ci-samples repo:

https://github.com/MichaelChirico/r-ci-samples/tree/master/pkgdown

The other advice here basically covers what you'll get from the r-ci-samples repo, the advantage is it's all in one place already, and also links a ton of other CI files from R packages (the disadvantage vs. live GitHub search is I am not particularly diligent about keeping the list of reference repos up to date).