message: add a link to the admission types
diff: //! For more information on admission controllers, see:
  //! https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/
  //! https://kubernetes.io/blog/2019/03/21/a-guide-to-kubernetes-admission-controllers/
  +//! https://github.com/kubernetes/api/blob/master/admission/v1/types.go
  use crate::{
  api::{DynamicObject, GroupVersionKind, GroupVersionResource, Resource, TypeMeta},
  