Update README.md

Author: TheBIMsider

README.md

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 A simple, web-based golf handicap calculator that helps golfers track their rounds and calculate their USGA Handicap Index. Built with vanilla HTML, CSS, and JavaScript, designed to be hosted on GitHub Pages with data storage via Google Sheets.
 
+> **📋 Demo Notice**: This live demo uses dummy golf data for demonstration purposes. To track your own golf rounds, you'll need to set up your own Google Sheets connection following the instructions below.
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 ## 🤖 AI-Powered Development
 
 This project was created as a "vibe coding" session using **Claude Sonnet 4** AI assistance, with human guidance and golf expertise provided by **Carl Storms** aka ["The BIMsider"](https://bio.link/thebimsider). Carl's unfortunately high golf scores serve as realistic test data throughout the examples! 🏌️‍♂️⛳