add extract command to readme

Author: florianbgt

README.md

@@ -117,6 +117,13 @@ manifest generated by `napi manifest generate`. This provides an interactive
 view of your codebase's architecture, helping you identify areas for potential
 improvements and refactoring.
 
+### `napi extract`
+
+Extract specific symbols (functions, classes, etc.) from your codebase into
+separate files. Use the format `--symbol file|symbol` where file is the path
+relative to your project root and symbol is the name to extract. The UI can
+generate these commands for convenient copy-pasting when browsing your code.
+
 > **Important**: Run `napi manifest generate` whenever you make significant
 > changes to your codebase to ensure your manifest stays up-to-date. The
 > manifest data can be integrated into CI/CD workflows to track architectural