Add nvidia/low-frame-rate-speech-codec-22khz model on docs
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beep boop 🤖: 🙏 The following files have warnings. In case you are familiar with these, please try helping us to improve the code base.

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Your code was analyzed with PyLint. The following annotations have been identified:

```
************* Module nemo.collections.tts.models.audio_codec
nemo/collections/tts/models/audio_codec.py:70:0: C0301: Line too long (169/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:198:0: C0301: Line too long (125/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:306:0: C0301: Line too long (129/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:654:0: C0301: Line too long (143/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:655:0: C0301: Line too long (172/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:661:0: C0301: Line too long (141/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:662:0: C0301: Line too long (171/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:668:0: C0301: Line too long (141/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:669:0: C0301: Line too long (171/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:675:0: C0301: Line too long (159/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:676:0: C0301: Line too long (180/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:682:0: C0301: Line too long (159/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:683:0: C0301: Line too long (180/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:689:0: C0301: Line too long (132/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:690:0: C0301: Line too long (145/119) (line-too-long)
nemo/collections/tts/models/audio_codec.py:48:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/tts/models/audio_codec.py:410:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:484:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:487:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:508:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:567:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:621:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/tts/models/audio_codec.py:628:4: C0116: Missing function or method docstring (missing-function-docstring)

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Your code has been rated at 9.22/10
```

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Thank you for improving NeMo's documentation! I think now the PR is ready to be merged :). Can you guys please review it? @rlangman @anteju  @blisc 
# What does this PR do ?

Add [nvidia/low-frame-rate-speech-codec-22khz](https://huggingface.co/nvidia/low-frame-rate-speech-codec-22khz) model on docs
