chore: add maintenance note

Author: rubenfonseca

aws_lambda_powertools/event_handler/util.py

@@ -5,6 +5,8 @@ class _FrozenDict(dict):
     This is needed because the default dict implementation is not hashable.
     The only usage for this right now is to store dicts as part of the Router key.
     The implementation only takes into consideration the keys of the dictionary.
+
+    MAINTENANCE: this is a temporary solution until we refactor the route key into a class.
     """
 
     def __hash__(self):