Add link to GridRefIter example (#2633)

src/iterators/intoiterator.md

@@ -76,12 +76,15 @@ The example iterates over all combinations of x and y coordinates.
 Try iterating over the grid twice in `main`. Why does this fail? Note that
 `IntoIterator::into_iter` takes ownership of `self`.
 
-Fix this issue by implementing `IntoIterator` for `&Grid` and storing a
-reference to the `Grid` in `GridIter`.
+Fix this issue by implementing `IntoIterator` for `&Grid` and creating a
+`GridRefIter` that iterates by reference. A version with both `GridIter` and
+`GridRefIter` is available [in this playground][1].
 
 The same problem can occur for standard library types: `for e in some_vector`
 will take ownership of `some_vector` and iterate over owned elements from that
 vector. Use `for e in &some_vector` instead, to iterate over references to
 elements of `some_vector`.
 
 </details>
+
+[1]: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=947e371c7295af758504f01f149023a1