Update arrow-array/src/array/mod.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: tustvold

arrow-array/src/array/mod.rs

@@ -79,6 +79,7 @@ pub use list_view_array::*;
 use crate::iterator::ArrayIter;
 
 mod private {
+    /// Private marker trait to ensure [`Array`] can not be implemented outside this crate
     pub trait Sealed {}
 
     impl<T: Sealed> Sealed for &T {}