Wav2Vec2 Fine-tuning Tutorial
Hi,

As you currently don't have a tutorial for training wav2vec2 #2342, I tried to create a new yaml file to train wav2vec2.
However, I didn't succeed and I need your guidance and help.

I have created a Colab example that replicate my experiment here:
https://colab.research.google.com/drive/1kJQA0wm7EVLGsDlZmhCv-2siXXJvTpUt?usp=sharing

This is the current error:
```
GPU available: True, used: True
TPU available: False, using: 0 TPU cores
[NeMo I 2021-06-25 14:10:52 exp_manager:216] Experiments will be logged at /content/nemo_experiments/Wav2vec_Pretrain/2021-06-25_14-10-52
[NeMo I 2021-06-25 14:10:52 exp_manager:563] TensorboardLogger has been set up
Traceback (most recent call last):
  File "wav2vec_pretrain.py", line 97, in <module>
    main()  # noqa pylint: disable=no-value-for-parameter
  File "/usr/local/lib/python3.7/dist-packages/nemo/core/config/hydra_runner.py", line 103, in wrapper
    strict=None,
  File "/usr/local/lib/python3.7/dist-packages/hydra/_internal/utils.py", line 347, in _run_hydra
    lambda: hydra.run(
  File "/usr/local/lib/python3.7/dist-packages/hydra/_internal/utils.py", line 201, in run_and_report
    raise ex
  File "/usr/local/lib/python3.7/dist-packages/hydra/_internal/utils.py", line 198, in run_and_report
    return func()
  File "/usr/local/lib/python3.7/dist-packages/hydra/_internal/utils.py", line 350, in <lambda>
    overrides=args.overrides,
  File "/usr/local/lib/python3.7/dist-packages/hydra/_internal/hydra.py", line 112, in run
    configure_logging=with_log_configuration,
  File "/usr/local/lib/python3.7/dist-packages/hydra/core/utils.py", line 127, in run_job
    ret.return_value = task_function(task_cfg)
  File "wav2vec_pretrain.py", line 92, in main
    wav2vec_encoder_model = Wav2VecEncoderModel(cfg=cfg.model, trainer=trainer)
  File "/usr/local/lib/python3.7/dist-packages/nemo/collections/asr/models/wav2vec/wav2vec_model.py", line 54, in __init__
    self.global_rank = 0
  File "/usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py", line 1178, in __setattr__
    object.__setattr__(self, name, value)
AttributeError: can't set attribute
```

Your feedback is highly appreciated.