Update README.md

README.md

@@ -18,8 +18,11 @@ classDiagram
   class Subject
   <<Abstract>> Subject
   Subject "1" --> "*" Observer
-  Subject : +attach(Observer)
-  Subject : +detach(Observer)
+  Subject : +attach(Observer) void
+  Subject : +detach(Observer) void
+  Subject : -notifyObservers() void
+  Subject : -notifyObservers(Object) void
+  
   class Observer
   <<interface>> Observer
 ```