add explanation of MMLU at the beginning of mmlu.py

It is good practice to include docstrings with clarifications.

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>

Author: makelinux

src/instructlab/eval/mmlu.py

@@ -1,5 +1,11 @@
 # SPDX-License-Identifier: Apache-2.0
 
+"""
+MMLU - Massive Multitask Language Understanding
+https://en.wikipedia.org/wiki/MMLU
+https://arxiv.org/abs/2009.03300
+"""
+
 # Standard
 from typing import Optional, Union
 import os