Added spanish translation of autoclass_tutorial.
# Translation of autoclass_tutorial.mdx into spanish

I made the translation of autoclass_turorial.mdx into Spanish (fixes #15947). The document is located in the docs/source/es folder.

This PR also includes the translation of _toctree.yml to include autoclass_tutorial.

FYI @omarespejel 


## 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? 
_The documentation is not available anymore as the PR was closed or merged._<|||||>LGTM! Just that little change in the `_toctree.yml`, @Duedme. Thanks!

Is it ok if I merge when the change is made @sgugger?