ensure that re-exported symbols show feature label in root (#754)

Co-authored-by: Toby Lawrence <[email protected]>

Author: GlenDC

tower/src/lib.rs

@@ -202,15 +202,20 @@ pub mod layer;
 
 #[cfg(feature = "util")]
 #[doc(inline)]
+#[cfg_attr(docsrs, doc(cfg(feature = "util")))]
 pub use self::util::{service_fn, ServiceExt};
 
 #[doc(inline)]
 pub use crate::builder::ServiceBuilder;
+
 #[cfg(feature = "make")]
 #[doc(inline)]
+#[cfg_attr(docsrs, doc(cfg(feature = "make")))]
 pub use crate::make::MakeService;
+
 #[doc(inline)]
 pub use tower_layer::Layer;
+
 #[doc(inline)]
 pub use tower_service::Service;