Add explicit example for RAG chat templating

[A-Duss]

What does this PR do?

As discussed with @Rocketknight1 in #33421, this commit updates the chat_templating documentation to:

• Clarify that the documents input is not yet supported by most models.
• Provide an example with a model that do support it.
• Offer guidance on how to check if a model supports the documents feature.

Hoping to improve readers understanding of the feature.

Might be beneficial to update the Spanish #28936, Japanese #28301 , Korean #20179 , and Chinese #26803 corresponding docs, I did not risk myself as I do not speak those languages fluently enough. es, ja, ko, zh

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.

Who can review?

Anyone in the community is free to review the PR once the tests have passed.
@stevhliu @Rocketknight1

[Rocketknight1]

This looks good! I ran the example successfully, and Command-R reported that "interestingly enough", man has always dreamed of destroying the moon. Definitely feel like it was wryly aware that the sources we'd given it might not have been entirely accurate, lol.

I made a suggestion to replace the section you added at the end with a Tip box, but other than that this should be ready to merge soon.

[stevhliu]

LGTM, thanks!

[A-Duss]

Thanks @Rocketknight1 for the tweaking, seemed simpler and clearer to me, I committed your suggestion. 😄
Should be ready to merge now. @stevhliu ? (not sure if I am supposed to @ you now, sorry if I am not)

[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.

[Rocketknight1]

Yes, it's ready to merge, and don't worry, I can approve it, since it's just a doc change.

Thank you, and congratulations on your first PR!