Added diagnostic for pin! macro in addition to Box::pin if Unpin isn't implemented

Author: ndrewxie

core/src/marker.rs

@@ -823,7 +823,7 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 /// [`pin` module]: crate::pin
 #[stable(feature = "pin", since = "1.33.0")]
 #[rustc_on_unimplemented(
-    note = "consider using `Box::pin`",
+    note = "consider using the `pin!` macro\nconsider using `Box::pin` if you need to access the pinned value outside of the current scope",
     message = "`{Self}` cannot be unpinned"
 )]
 #[lang = "unpin"]