windows_subsystem isn't documented anywhere

[Xaeroxe]

The feature made available at #37499 isn't documented in the rust book, the cargo book, or the std library documentation. It's not clear how people are supposed to discover this without combing the RFCs.

[Xaeroxe]

Nevermind, found it https://doc.rust-lang.org/reference/runtime.html#the-windows_subsystem-attribute