Added keyboardHeight property to useKeyboard

The keyboardHeight property was documented in the [README](https://github.com/react-native-community/react-native-hooks/blob/master/README.md#usekeyboard) however was missing in the actual useKeyboard hook

Author: DaniAkash

src/useKeyboard.ts

@@ -10,20 +10,23 @@ export default function useKeyboard() {
     start: { screenX: 0, screenY: 0, width: 0, height: 0 },
     end: { screenX: 0, screenY: 0, width: 0, height: 0 },
   })
+  const [keyboardHeight, setKeyboardHeight] = useState<number>(0)
 
   const handleKeyboardWillShow: KeyboardEventListener = (e) => {
     setCoordinates({ start: e.startCoordinates, end: e.endCoordinates })
   }
   const handleKeyboardDidShow: KeyboardEventListener = (e) => {
     setShown(true)
     setCoordinates({ start: e.startCoordinates, end: e.endCoordinates })
+    setKeyboardHeight(e.endCoordinates.height)
   }
   const handleKeyboardWillHide: KeyboardEventListener = (e) => {
     setCoordinates({ start: e.startCoordinates, end: e.endCoordinates })
   }
   const handleKeyboardDidHide: KeyboardEventListener = (e) => {
     setShown(false)
     setCoordinates({ start: e.startCoordinates, end: e.endCoordinates })
+    setKeyboardHeight(0)
   }
 
   useEffect(() => {
@@ -55,5 +58,6 @@ export default function useKeyboard() {
   return {
     keyboardShown: shown,
     coordinates,
+    keyboardHeight
   }
 }