Refactor ArgumentParser arguments in emformer_rnnt recipes (#2236)

Summary:
Replace underscore with dash in ArgumentParser's arguments.

Pull Request resolved: https://github.com/pytorch/audio/pull/2236

Reviewed By: mthrok

Differential Revision: D34266977

Pulled By: nateanl

fbshipit-source-id: ceacac12c04016a8dbf2a1a7d6bbcf65d4d53d21

examples/asr/emformer_rnnt/README.md

@@ -30,7 +30,7 @@ srun --cpus-per-task=12 --gpus-per-node=8 -N 4 --ntasks-per-node=8 python train.
 
 Sample SLURM command for evaluation:
 ```
-srun python eval.py --model_type librispeech --checkpoint_path ./experiments/checkpoints/epoch=119-step=208079.ckpt --dataset-path ./datasets/librispeech  --sp-model-path ./spm_bpe_4096.model --use-cuda
+srun python eval.py --model-type librispeech --checkpoint-path ./experiments/checkpoints/epoch=119-step=208079.ckpt --dataset-path ./datasets/librispeech  --sp-model-path ./spm_bpe_4096.model --use-cuda
 ```
 
 The script used for training the SentencePiece model that's referenced by the training command above can be found at [`librispeech/train_spm.py`](./librispeech/train_spm.py); a pretrained SentencePiece model can be downloaded [here](https://download.pytorch.org/torchaudio/pipeline-assets/spm_bpe_4096_librispeech.model).

examples/asr/emformer_rnnt/global_stats.py

 """Generate feature statistics for training set.
 
 Example:
-python global_stats.py --model_type librispeech --dataset_path /home/librispeech
+python global_stats.py --model-type librispeech --dataset-path /home/librispeech
 """
 
 import json

examples/asr/emformer_rnnt/pipeline_demo.py

@@ -67,9 +67,9 @@ def run_eval_streaming(args):
 
 def parse_args():
     parser = ArgumentParser()
-    parser.add_argument("--model_type", type=str, choices=[MODEL_TYPE_LIBRISPEECH, MODEL_TYPE_TEDLIUM3], required=True)
+    parser.add_argument("--model-type", type=str, choices=[MODEL_TYPE_LIBRISPEECH, MODEL_TYPE_TEDLIUM3], required=True)
     parser.add_argument(
-        "--dataset_path",
+        "--dataset-path",
         type=pathlib.Path,
         help="Path to dataset.",
         required=True,