fix(docs): use correct GitHub username in clone URL

Change placeholder YOUR_USERNAME to crumplecup in git clone example.

Files modified:
- CONTRIBUTING.md - Updated git clone URL

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: crumplecup

CONTRIBUTING.md

@@ -146,7 +146,7 @@ Want to contribute code? Awesome! Here's everything you need to know.
 
 ```bash
 # Fork and clone the repo
-git clone https://github.com/YOUR_USERNAME/arcgis.git
+git clone https://github.com/crumplecup/arcgis.git
 cd arcgis
 
 # Install development tools