readme update

Author: underthestars-zhy

README.md

@@ -24,6 +24,10 @@ IconChanger is an app that can change you app's icon. It simplifies your icon ch
 8. Open IconChanger Setting
 9. Input the host.
 
+## About System App
+
+Vert sorry to tell, but currtely we cannot change the icon of System Apps. Because of the SIP, users or root cannot write things to this kind of apps. And the idea of Bridge App need to change the `Info.plist`, so it will not work.
+
 ## How to contribute
 
 1. Fork the project