supported python versions reference
# What does this PR do?

Provides a reference to the supported python versions to get a development environment working.

Fixes #18112


## 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.
- [x] 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?
@sgugger 

_The documentation is not available anymore as the PR was closed or merged._<|||||>@sgugger another thing to consider is that we are only referencing the line number so the moment the file is updated, and the lines shift it will link to something else. Any fixes come to mind? Or will that do for the time being?