fix some missing information for metric:_answer_nli_correctness

[faneshion]

@QianHaosheng update this metric by adding the missing informations.

rageval/rageval/metrics/_answer_nli_groudedness.py

Line 19 in 1408f9b

AnswerNLIGroundedness is the metric build based on NLI model.

Note that all metrics should be implemented with detailed information. Below is an example from huggingface.datasets.metric:
https://github.com/huggingface/datasets/blob/2.17.1/metrics/accuracy/accuracy.py