[skip ci] Recommend LLM disclosure for GH comments (GH-21506)

Author: iluuu1994

CONTRIBUTING.md

@@ -27,6 +27,7 @@ had several contributions accepted, commit privileges are often quickly granted.
 * [Git commit rules](#git-commit-rules)
 * [Copyright and license headers](#copyright-and-license-headers)
 * [NEWS file](#news)
+* [LLM usage in GitHub comments](#llm-usage-in-github-comments)
 
 ## Pull requests
 
@@ -537,6 +538,12 @@ If for some reason a feature is introduced in a branch lower than master,
 although this is strictly prohibited by other policies, then the entry must
 also be in master.
 
+## LLM usage in GitHub comments
+
+When using LLMs to generate comments to maintainers for any purpose other than
+direct translation, we would highly appreciate it if you disclosed the relevant
+paragraphs as such via markdown quote.
+
 ## Thanks
 
 Thank you for contributing to PHP!