Update readme with how to train offline and fix BPE command
# What does this PR do?

Just some minor updates to the README with how to do offline training and fixed the BPE command to allow for easy copy and paste.

@lvwerra 

_The documentation is not available anymore as the PR was closed or merged._<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15897). All of your documentation changes will be reflected on that endpoint.<|||||>@lvwerra thanks for the edits, it reads a lot better!<|||||>Awesome, thanks for integrating the changes. There seems to be one comment still open? Do you disagree there or should we integrate it as well?<|||||>@lvwerra whoops, completely missed that comment 😅 just added it 😃<|||||>@ncoop57 Is it possible that you just closed the comment without applying it? 😃 <|||||>> @ncoop57 Is it possible that you just closed the comment without applying it? 😃

🤦 this is why I should not manage PRs from the GitHub app 😅. Okay @lvwerra , I think I commited all the changes 🤞<|||||>Looks good - feel free to merge it when you are ready and all the checks have passed. 🚀 