Use onInput instead of onChange in the README example (#3420)

The preact documentation recommends it.

README.md

@@ -89,7 +89,7 @@ const App = () => {
 	return (
 		<div>
 			<p>Do you agree to the statement: "Preact is awesome"?</p>
-			<input value={input} onChange={e => setInput(e.target.value)} />
+			<input value={input} onInput={e => setInput(e.target.value)} />
 		</div>
 	)
 }