Clarify WindowsMut (Lending)Iterator

fixes 133628

Author: hkBst

library/core/src/slice/mod.rs

@@ -1099,10 +1099,12 @@ impl<T> [T] {
     /// assert!(iter.next().is_none());
     /// ```
     ///
-    /// There's no `windows_mut`, as that existing would let safe code violate the
-    /// "only one `&mut` at a time to the same thing" rule.  However, you can sometimes
-    /// use [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
+    /// There's no `windows_mut` Iterator-equivalent of `windows`,
+    /// (as `[0,1,2].windows_mut(2).collect()` would create 2 mutable references to the middle elements of that array),
+    /// though a [LendingIterator]-equivalent is possible.
+    /// However, you can sometimes use [`Cell::as_slice_of_cells`](crate::cell::Cell::as_slice_of_cells) in
     /// conjunction with `windows` to accomplish something similar:
+    /// [LendingIterator]: https://blog.rust-lang.org/2022/10/28/gats-stabilization.html
     /// ```
     /// use std::cell::Cell;
     ///