Push to hub save
# What does this PR do?

This PR changes the documentation of the `push_to_hub` training argument to be in sync with the actual behavior, and also makes sure that when `push_to_hub=True`, a push is done every time the model is saved.

Fixes #15313
_The documentation is not available anymore as the PR was closed or merged._<|||||>I think you're missing the fact that, apart from a push asked explicitly with `trainer.push_to_hub()` (or now `trainer.save_model()`) all other pushes are only done if the previous one is completely finished (see [here](https://github.com/huggingface/transformers/blob/637e81752aad01738d36ef816fadee21fa392317/src/transformers/trainer.py#L2712)). So, there are no frequent pushes (except if the user asks for it by putting `trainer.save_model()` in a loop but I don't think that will happen).<|||||>Then that's perfect :) <|||||>Ugh, sorry @osanseviero I was convinced I had accepted your suggestions before merging (must have skipped one click), will make a new commit with you as Co-author...