Update doc for revision and token
# What does this PR do?

This PR updates the docstrings of all `from_pretrained` methods to:
- adapt the documentation for `use_auth_token`
- remove the Tip about `use_auth_token=True` for private models
- add a tip about checking out PRs using the revision argument

(For now just did the changes on the config but will copy paste everywhere once I have had opinions :-) )
_The documentation is not available anymore as the PR was closed or merged._