PR summary

This adds a short note in the "Policies and guidelines" section of doc/devel/index.rst that directs contributors to the existing “Restrictions on Generative AI Usage” guidance (the generative_ai reference in contribute.rst).

Why is this change necessary?

• New contributors may not see the AI usage policy unless they happen to read contribute.rst in full.
• The "Policies and guidelines" page is where we already tell people how to contribute responsibly, so it's the natural place to surface that policy.

What problem does it solve?

• It makes the AI usage expectations visible at the point where contributors first learn about review, triage, maintenance, and process.
• This directly addresses issue [Doc]: Link AI policy on contributing page #30439.

What is the reasoning for this implementation?

• We insert a two-line paragraph immediately before the existing .. grid:: block in the "Policies and guidelines" section, pointing to the existing :ref:\generative_ai`` anchor. No new content is invented, and no other structure is changed.

Additionally:

• Title summarizes the change: DOC: Link AI policy from developer guide index (#30439).
• This is documentation-only, no behavior change and no code/API change.

PR checklist

• "closes [Doc]: Link AI policy on contributing page #30439" is in the body of the PR description to link the related issue
• [N/A] new and changed code is tested
• [N/A] Plotting related features are demonstrated in an example
• [N/A] New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines