doc: link to Mathlib AI policy in CONTRIBUTING.md (#593)

For some time we have followed the Mathlib guideline of disclosing AI
usage in PR descriptions, but this was not documented in
`CONTRIBUTING.md`. This PR adds a mention of this and links to the new
Mathlib AI policy.

---------

Co-authored-by: Fabrizio Montesi <famontesi@gmail.com>

Author: chenson2018

CONTRIBUTING.md

@@ -2,6 +2,7 @@
 
 - [Contributing to CSLib](#contributing-to-cslib)
 - [Contribution model](#contribution-model)
+- [The role of AI](#the-role-of-ai)
 - [Style and documentation](#style-and-documentation)
   - [Variable names](#variable-names)
   - [Proof style and golfing :golf:](#proof-style-and-golfing-golf)
@@ -38,8 +39,6 @@
       - [Back ends for Boole](#back-ends-for-boole)
       - [Implementing verification paradigms](#implementing-verification-paradigms)
       - [Lean automation](#lean-automation)
-      - [The role of AI](#the-role-of-ai)
-
 
 # Contributing to CSLib
 
@@ -57,6 +56,11 @@ If you are adding something new to CSLib and are in doubt about it, you are very
 
 If you are unfamiliar with CSLib as a whole and want to understand how to get started, please see [Getting started](#getting-started).
 
+# The role of AI
+
+CSLib in general follows the Mathlib policy on [use of AI](https://leanprover-community.github.io/contribute/index.html#use-of-ai). In particular, take note of:
+> If you use artificial intelligence [...] please explain this in the PR description. Explain which tool(s) you used and how you used it. This provides useful context for reviewers: tools make different mistakes than humans, so knowing this makes it easier to spot common errors.
+
 # Style and documentation
 
 We generally follow the [mathlib style for coding and documentation](https://leanprover-community.github.io/contribute/style.html), so please read that as well. Some things worth mentioning and conventions specific to CSLib are explained next.
@@ -322,12 +326,3 @@ The formal methods community has a wide range of verification techniques that co
 Since Boole back ends reduce correctness questions to Lean conjectures, automation is central.
 
 We already rely on key techniques such as `grind` and `lean-smt`. Additional work on automation for conjectures generated from Boole is welcome, including domain-specific automation that remains performant and readable.
-
-#### The role of AI
-
-There are two primary areas where generative AI can help:
-
-- generating/refining specifications (at the front-end or Boole level)
-- helping to prove Lean conjectures
-
-Other creative uses of AI are welcome, but contributions should remain reviewable and maintainable.