Add alternative solution in advanced-forward challenge

"from __future__ import annotations"

Author: LoicRiegel

challenges/advanced-forward/solution.py

@@ -8,6 +8,19 @@ def copy(self) -> "MyClass":
         return copied_object
 
 
+# Alternative soltion:
+#
+# from __future__ import annotations
+# class MyClass:
+#     def __init__(self, x: int) -> None:
+#         self.x = x
+# 
+#     # TODO: Fix the type hints of `copy` to make it type check
+#     def copy(self) -> MyClass:
+#         copied_object = MyClass(x=self.x)
+#         return copied_object
+
+
 ## End of your code ##
 
 from typing import assert_type