docs: doc expectations of ai-assisted contributions (#3051)

A lot of this should go without saying, but I want to have a written
reference we
can refer to and so it's clear to potential contributors.

The two basic points it makes is that AI-assisted contributions are
allowed, but
they're treated no different than regular contributions, so all the
usual expectations
apply.

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

CONTRIBUTING.md

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 324801c..8f985c5 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -318,6 +318,25 @@
   * Changing internal details, such as renaming an internal file.
   * Changing a rule to a macro.
 
+## AI-assisted Contributions
+
+Contributions assisted by AI tools are allowed. However, the human author
+submitting the pull request is responsible for the contributed code as if they
+had written it entirely themselves. This means:
+
+*   **Understanding the code:** You must be able to explain what the code does
+    and why it's implemented that way. This includes discussing its
+    implications, and any trade-offs made during its development, just as if you
+    had written it entirely yourself.
+*   **Vetting the correctness and functionality:** You are responsible for
+    thoroughly testing and verifying that the code is correct, functional, and
+    meets all project requirements and standards.
+
+If the human PR author cannot fulfill these responsibilities, the `rules_python`
+maintainers will not spend time reviewing or merging the PR. The goal is to
+ensure that all contributions, regardless of their origin, maintain the quality
+and integrity of the project and do not place an undue burden on maintainers.
+
 ## FAQ
 
 ### Installation errors when during `git commit`