Add useTimeout snippet

snippets/useInterval.md

@@ -8,7 +8,7 @@ A hook that implements `setInterval` in a declarative manner.
 - Create a custom hook that takes a `callback` and a `delay`.
 - Use the `React.useRef()` hook to create a `ref` for the callback function.
 - Use the `React.useEffect()` hook to remember the latest callback.
-- Use the `Rect.useEffect()` hook to set up the interval.
+- Use the `Rect.useEffect()` hook to set up the interval and clean up.
 
 
 ```jsx