[docs] set overflowing image width to auto-scale
# What does this PR do?

The image shown below overflowed on small screens. A simple inline-css to set the same width as its div solved the problem.
before | after
------- | -------
![Screenshot_20221115_032312_Chrome.jpg](https://user-images.githubusercontent.com/29195190/201737154-59876bf8-1d71-494f-a25f-015a0636d382.jpg) | ![Screenshot_20221115_032216_Chrome.jpg](https://user-images.githubusercontent.com/29195190/201737194-a23a28a8-71f7-4042-94c3-076c32288de8.jpg)

Fixes #20196 


## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? 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](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?
Hello @sgugger, may you please review this simple PR?

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20197). All of your documentation changes will be reflected on that endpoint.<|||||>Thanks for fixing this, it looks good to me!
@LysandreJik Do you mind double-checking?<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20197). All of your documentation changes will be reflected on that endpoint.<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20197). All of your documentation changes will be reflected on that endpoint.