[isort] add known 3rd party to setup.cfg (#4053)

* add known 3rd party to setup.cfg

* comment

* Update CONTRIBUTING.md

Co-authored-by: Julien Chaumond <chaumond@gmail.com>

examples/translation/t5/evaluate_wmt.py

@@ -2,9 +2,9 @@ import argparse
 from pathlib import Path
 
 import torch
+from sacrebleu import corpus_bleu
 from tqdm import tqdm
 
-from sacrebleu import corpus_bleu
 from transformers import T5ForConditionalGeneration, T5Tokenizer