[Docs] Add Authentication Note and Link to Guided Tour in Quick Demo Section

[yuka-with-data]

The current Quick demo section in the smolagents README does not mention that authentication may be necessary for certain use cases, especially when using HfApiModel. This can lead to confusion when users encounter errors or when trying to access gated models.

Suggested Change

Add a short note in the Quick demo section explaining that:

• Users may need to authenticate to avoid rate limits or access gated models.
• Link to Guided Tour for detailed instructions on how to set the token.

Why This is Important

• Helps new users avoid common errors
• Ensures smoother onboarding experience