Update WhisperTokenizer Doc: Timestamps and Previous Tokens Behaviour

[bruno-hays]

What does this PR do?

#32378

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@ylacombe

[ylacombe]

Super clear! Thanks for taking care of this!

For the CI tests to pass, you should also:

1. rebase the branch
2. apply your modification to the fast whisper tokenizer (you can simply do make fix-copies)
3. reformate for quality. To do and as per the contributing guide, you only have to install the right dependencies (pip install -e ".[quality]") and to apply style correction (make fixup)

[bruno-hays]

Thanks @ylacombe !
I ran into some issues running make fixup due to it needing both torch and tensorflow.
But I get this before it crashes:

Checking/fixing src/transformers/models/whisper/tokenization_whisper.py src/transformers/models/whisper/tokenization_whisper_fast.py
All checks passed!
2 files left unchanged
python utils/custom_init_isort.py
python utils/sort_auto_mappings.py
python utils/check_doc_toc.py --fix_and_overwrite
running deps_table_update
updating src/transformers/dependency_versions_table.py
python utils/check_copies.py
python utils/check_table.py
python utils/check_dummies.py
python utils/check_repo.py

I hope it means it's ok, no file changed

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[LysandreJik]

Thank you!