Add documentation on lack of validation for container nodes

docs/source/structured_config.rst

@@ -353,6 +353,18 @@ Interpolated values are validated, and converted when possible, to the annotated
     >>> cfg.str_key = "1234"  # string value
     >>> assert cfg.int_key == 1234  # automatically convert str to int
 
+Note however that this validation step is currently skipped for container node interpolations:
+
+.. doctest::
+
+    >>> @dataclass
+    ... class NotValidated:
+    ...     some_int: int = 0
+    ...     some_dict: Dict[str, str] = II("some_int")
+
+    >>> cfg = OmegaConf.structured(NotValidated)
+    >>> assert cfg.some_dict == 0  # type mismatch, but no error
+
 
 Frozen
 ^^^^^^