Update intro-react.md

Author: gaearon

docs/intro-react.md

@@ -394,7 +394,7 @@ Now, when someone presses the button, `onPress` will fire, calling the `setIsHun
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-> You might’ve noticed that although `isHungry` is a [const](https://developer.mozilla.org/Web/JavaScript/Reference/Statements/const), it is seemingly reassignable! What is happening is when a state-setting function like `setIsHungry` is called, its component will re-render. In this case the `Cat` function will run again with the new value of `isHungry`, and return a `<Button>` with the new `title`!
+> You might’ve noticed that although `isHungry` is a [const](https://developer.mozilla.org/Web/JavaScript/Reference/Statements/const), it is seemingly reassignable! What is happening is when a state-setting function like `setIsHungry` is called, its component will re-render. In this case the `Cat` function will run again, and this time, `useState` will give us the next value of `isHungry`, which we use to render the `<Button>`. The old value is discarded when we set the state!
 
 Finally, put your cats inside a `Cafe` component: