extension: fix README.md and update UpdateRegisteredExtension

Author: weizhouapache

api/src/main/java/com/cloud/event/EventTypes.java

@@ -846,6 +846,7 @@ public class EventTypes {
     public static final String EVENT_EXTENSION_DELETE = "EXTENSION.DELETE";
     public static final String EVENT_EXTENSION_RESOURCE_REGISTER = "EXTENSION.RESOURCE.REGISTER";
     public static final String EVENT_EXTENSION_RESOURCE_UNREGISTER = "EXTENSION.RESOURCE.UNREGISTER";
+    public static final String EVENT_EXTENSION_RESOURCE_UPDATE = "EXTENSION.RESOURCE.UPDATE";
     public static final String EVENT_EXTENSION_CUSTOM_ACTION_ADD = "EXTENSION.CUSTOM.ACTION.ADD";
     public static final String EVENT_EXTENSION_CUSTOM_ACTION_UPDATE = "EXTENSION.CUSTOM.ACTION.UPDATE";
     public static final String EVENT_EXTENSION_CUSTOM_ACTION_DELETE = "EXTENSION.CUSTOM.ACTION.DELETE";