✏️ docs: Add training guide and improve documentation consistency

[baptistecolle]

📝 Enhance documentation clarity and structure: Add comprehensive training guide and fix inconsistencies

Overview

This PR addresses several documentation issues and improvements:

1. Adds a new training documentation page for the huggingface docs website

• This was previsouly missing and not up to date with the repo

2. Resolves documentation inconsistencies

Motivation

Our documentation needed more clarity and structure around training capabilities, while some sections had inconsistent or incomplete information that could confuse users.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[tengomucho]

Thanks for your first contribution on the project! 🥳 Few nits and we can merge.

[tengomucho]

you can remove the wip here

[tengomucho]

it is actually called v5e, see https://cloud.google.com/tpu/docs/v5e

[baptistecolle]

There is also v5p that's why i wanted to say v5 directly, but with #108 this sentence is actually removed to make it more general

[tengomucho]

In theory we could support v5p, but we haven't done any testing on that platform yet. You can remove the sentence as done on #108 and they will rebase later.

[tengomucho]

I think there is no need to add this

[baptistecolle]

@tengomucho Based on #108, it seems we should also make the documentation less v5-specific. Should we update it now or keep it as it is?