error: unknown `doc` attribute `include`
  --> $DIR/doc-include-suggestion.rs:1:7
   |
LL | #[doc(include = "external-cross-doc.md")]
   | ------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-- help: use `doc = include_str!` instead: `#[doc = include_str!("external-cross-doc.md")]`
   |
   = note: `#[deny(invalid_doc_attributes)]` on by default

error: aborting due to 1 previous error