Add a sitrep function?

[maelle]

Like usethis::git_sitrep(). It would tell you whether pkgcheck can find ctags for instance.

[mpadge]

First need ropensci-review-tools/pkgstats#65. But I also think, especially with the help of @kellijohnson-NOAA via #270 that that information will be generated when needed anyway. I'm not sure there's much else that we'd put in a sitrep here? Any suggestions @maelle ?

[maelle]

A good thing with a sitrep function is that it's standalone, you can run it from anywhere to check your installation / help someone help you.