docs(README.mD): mention not drop in replacement

Author: rwieruch

README.md

@@ -96,6 +96,9 @@ export default App;
 ## Pitfalls
 
 * When a state update is called with the current value and optimized away, the callback is never called.
+* `useStateWithCallbackLazy` calls the callback with the scope that existed before update, while this.setState callback can access the updated this.state and `get something()` computed values. This can't be fixed, but it's a problem for people who expect a drop-in replacement.
+
+
 ## Contribute
 
 - `git clone [email protected]:the-road-to-learn-react/use-state-with-callback.git`