Update TF fine-tuning docs
This PR updates the fine-tuning sidebar tutorial with modern TF methods that were added in the most recent release.
_The documentation is not available anymore as the PR was closed or merged._<|||||>@stevhliu is there a better way to format a link to the `prepare_tf_dataset` docs [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18654/en/training#loading-data-as-a-tfdatadataset) than the way I did it here? It prints the whole `TFPreTrainedModel.prepare_tf_dataset` text, which looks a bit ugly on the page!<|||||>Yes, I believe you can just squiggly it!

[`~TFPreTrainedModel.prepare_tf_dataset`]<|||||>@stevhliu Thank you for the suggestions! I'll make more edits to incorporate the other bits and ping you again for a final look.<|||||>@sgugger @stevhliu I finished incorporating your edits and did some other cleanup. I also replaced `to_tf_dataset` in the other fine-tuning pages. I didn't touch the translations, though - should I edit those too?<|||||>@sgugger I tried those edits but it looked a little odd because there was no separate header for the PyTorch section. I added a `Train` header to the whole thing with a brief intro, and then a `Train with PyTorch Trainer` header inside that block, which I think works a little better and makes it easier for people to find what they want in the sidebar. Let me know what you think!<|||||>@sgugger :facepalm: I knew I'd regret pinging you before waiting for the job to finish and checking it myself. Fixed!