Document when this workaround can be removed

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/aresource.py

@@ -28,6 +28,8 @@ from translate.storage.jsonl10n import JsonFile as JsonFileTT
 class JsonFile(JsonFileTT):
     """
     Workaround ttkit bug on not including added units in saved file.
+
+    This is fixed in 1.13.0
     """
     def __str__(self):
         data = {}