Add VitePress cache to .gitignore

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -4,4 +4,7 @@ dist
 *.tsbuildinfo
 
 .env
-.env.local
+.env.local
+
+# VitePress cache
+docs/.vitepress/cache