Add Welcome heading above introduction paragraph

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: metalllinux

docs/guides/contribute/contributing.md

@@ -13,6 +13,8 @@ tags:
 
 This document was created with the assistance of AI. All content has been reviewed, tested, and verified by a human author. The author takes full responsibility for the accuracy and correctness of this document.
 
+## Welcome
+
 Thank you for your interest in contributing to the Rocky Linux documentation. This guide walks you through everything you need to create, edit, and submit documentation that meets our standards.
 
 ## Table of Contents