Added a note about to_config() constraints

Signed-off-by: Elena Khaustova <ymax70rus@gmail.com>

kedro/io/kedro_data_catalog.py

@@ -378,9 +378,14 @@ def to_config(
         dict[str, str | None],
         str | None,
     ]:
-        """Converts the KedroDataCatalog instance into a configuration format suitable for
+        """Converts the `KedroDataCatalog` instance into a configuration format suitable for
         serialization. This includes datasets, credentials, and versioning information.
 
+        This method is only applicabe to catalogs that contain datasets initialized with static, primitive
+        parameters. For example, it will work fine if one passes credentials as dictionary to
+        `GBQQueryDataset` but not as `google.auth.credentials.Credentials` object. See
+        https://github.com/kedro-org/kedro-plugins/issues/950 for the details.
+
         Returns:
             A tuple containing:
                 catalog: A dictionary mapping dataset names to their unresolved configurations,