Add uninstall action

manifest.jps

@@ -35,6 +35,12 @@ onInstall:
       Add-on installed successfully! 
       To create additional SFTP accounts, click on the "Add new SFTP user" button.    
 
+onUninstall:
+  - cmd[cp]: sudo rm -f ./add-sftp.sh
+  - return:
+      result: 0
+      message: "Add-on uninstalled successfully and script file removed."
+
 actions:
   add_sftp_user:
     - cmd[cp]: sudo ./add-sftp.sh