How to document S7 classes/generics?

[Sage0614]

I am using S7 class in my own package, currently seems there's no material I can find about how to properly document properties with a S7 class in roxygen2 style, and I got a lot of warnings of undocumented arguments when I run devtools::check(), It would be helpful to have a vignette that how S7 class and instance from S7 class should be documented when building packages upon them, so we have some approach we agreed on.

[hadley]

I've filed an issue to add S7 support to roxygen2: r-lib/roxygen2#1484

But I'll keep this issue open because it'll be good to discuss how we expect the .Rd files for S7 classes, generics, and methods to look.