Improve installation documentation about GestureHandlerRootView

[francois-pasquier]

Maybe I was distracted when I followed the installation instructions but I think this example should include the styling flex: 1

export default function App() {
  return <GestureHandlerRootView>{/* content */}</GestureHandlerRootView>;
}

Putting it as the end of the INFO section makes it easy to miss imo : )

[SMhdAsadi]

It is not required to put flex:1 for any GestureHandlerRootView. I think this is why they didn't put it here.

[hirbod]

Not aware of any app that would work without flex: 1 (or flexGrow: 1)