feat: Added iterators5.rs exercise.

info.toml

@@ -741,6 +741,21 @@ a mutable variable. Or, you might write code utilizing recursion
 and a match clause. In Rust you can take another functional
 approach, computing the factorial elegantly with ranges and iterators."""
 
+[[exercises]]
+name = "iterators5"
+path = "exercises/standard_library_types/iterators5.rs"
+mode = "test"
+hint = """
+The documentation for the std::iter::Iterator trait contains numerous methods
+that would be helpful here.
+
+Return 0 from count_stack to make the code compile in order to test count.
+
+The stack variable in count_stack is a slice of HashMaps. It needs to be
+converted into an iterator in order to use the iterator methods.
+
+The fold method can be useful in the count_stack function."""
+
 # THREADS
 
 [[exercises]]