Updating model card for wav2vec2
Author: AshAnand34
Pull request: yes

# What does this PR do?

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This pull request updates the `wav2vec2` documentation to improve readability, enhance usability with examples, and reorganize the structure for better navigation. Key changes include the addition of usage examples, restructuring of the API reference, and updates to the model overview.

### Documentation Enhancements:
* Replaced the abstract with a concise explanation of Wav2Vec2 and added links to Hugging Face Hub for checkpoints and examples.
* Added Python code examples demonstrating how to use the Wav2Vec2 model for automatic speech recognition and audio classification.
* Included guidance on using Flash Attention 2 for faster inference and quantization techniques for memory optimization.

### Structural Improvements:
* Reorganized the API reference section by converting model components (`Wav2Vec2Config`, `Wav2Vec2CTCTokenizer`, etc.) into subsections for better navigation.

These changes make the documentation more user-friendly and accessible, especially for developers new to Wav2Vec2.

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#36979

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).

## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@stevhliu

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker
- vision models: @amyeroberts, @qubvel
- speech models: @eustlb
- graph models: @clefourrier

Library:

- flax: @gante and @Rocketknight1
- generate: @zucchini-nlp (visual-language models) or @gante (all others)
- pipelines: @Rocketknight1
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @zach-huggingface, @SunMarc and @qgallouedec
- chat templates: @Rocketknight1

Integrations:

- deepspeed: HF Trainer/Accelerate: @SunMarc @zach-huggingface
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc @MekkCyber

Documentation: @stevhliu

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @Rocketknight1
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
- TensorFlow: @Rocketknight1

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Comments:
> Thanks!
> 
> Please apply some of these same changes (such as changing the API reference) to your other PRs 🤗 

I am out of town at the moment. I will make the changes when I am back.