Clarify stride option
# What does this PR do?

Clarify the `stride` option which refers to the number of overlapping tokens between chunks.

Fixes #22391


## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      Pull Request section?
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      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


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_The documentation is not available anymore as the PR was closed or merged._<|||||>@Narsil, I just added a sentence in the doc to avoid confusion about the naming.

Have a good day