Consider clarifying which dependents to check

[igordot]

Since I am posting an issue anyway, I just wanted to mention how helpful this package is. It's a big improvement over the local revdepcheck.

I think it would be helpful to add some text about which dependents to check. Currently, the two options are strong and most. I had to do a bit of digging to find that this parameter is passed to tools::package_dependencies():

a character vector listing the types of dependencies, a subset of c("Depends", "Imports", "LinkingTo", "Suggests", "Enhances"). Character string "all" is shorthand for that vector, character string "most" for the same vector without "Enhances", character string "strong" (default) for the first three elements of that vector.