Update README.md

README.md

@@ -99,7 +99,8 @@ The leaderboard is regularly updated and can be accessed at https://famma-bench.
 ##  Dataset Structure 
 
 ### features
-- question_id: a unique identifier for the question across the whole dataset.
+- idx：a unique identifier for the index of the question in the dataset.
+- question_id: a unique identifier for the question across the whole dataset: {language}_{main_question_id}_{sub_question_id}_{release_version}.
 - context: relevant background information related to the question.
 - question: the specific query being asked.
 - options: the specific query being asked.