Update README.md

Author: Zhang-JiahangH

README.md

@@ -7,6 +7,9 @@ High-performance React diff viewer for **large text/code files** with virtualize
 - 📊 Benchmark report: [benchmark-results/results.md](./benchmark-results/results.md)
 - 🇨🇳 中文文档: [README.zh-CN.md](./README.zh-CN.md)
 
+## Demo
+![20260408-024125](https://github.com/user-attachments/assets/5345cbe4-04b1-4cfd-bcba-a68fcd7e82aa)
+
 ## Why react-virtualized-diff
 
 Most diff components are smooth for small files, but degrade heavily with 10k+ lines.