[v4][docs][showcases] starter kit (#5725)

Hey, it is me again 🙂So I am just updating the docs due to some changes to my [starter](https://github.com/kanzitelli/react-native-navigation-starter) which are upgrading RNN to v4 and adding implementation of app logic using [MobX State Tree](https://github.com/mobxjs/mobx-state-tree) as an alternative to Redux.

docs/docs/showcases.md

@@ -14,7 +14,7 @@ It is a tab-based app and utilizes Split Layout for iOS tablets, 3D touch and mo
 ## Starter Kits
 * [atoami/react-native-navigation-redux-starter-kit](https://github.com/atoami/react-native-navigation-redux-starter-kit) - React Native Navigation(v2) Starter Kit with Redux, Saga, ESLint, Babel and Jest 😎
 * [alexwasner/react-native-mobx-firebase-starter](https://github.com/alexwasner/react-native-mobx-firebase-starter) - A React Native starter app with React Native Navigation(v2), MobX, Firebase, Lottie and More 🤓
-* [kanzitelli/react-native-navigation-starter](https://github.com/kanzitelli/react-native-navigation-starter) - Simple yet practical starter with React Native Navigation (**v3**), [Redux](https://github.com/reduxjs/redux) and more goodies such as Typescript, [RNN Hooks](https://github.com/underscopeio/react-native-navigation-hooks), [RN Vector Icons](https://github.com/oblador/react-native-vector-icons), [RN Gesture Handler](https://github.com/kmagiera/react-native-gesture-handler), [Redux Saga](https://github.com/redux-saga/redux-saga) and [Persist](https://github.com/rt2zz/redux-persist). As an example, basic Reddit App implemented inside.
+* [kanzitelli/react-native-navigation-starter](https://github.com/kanzitelli/react-native-navigation-starter) - Simple yet practical starter with React Native Navigation (**v4**), [MobX-State-Tree](https://github.com/mobxjs/mobx-state-tree) and [Redux](https://github.com/reduxjs/redux) (pick one) and more goodies inside such as Typescript, [RNN Hooks](https://github.com/underscopeio/react-native-navigation-hooks), [RN Vector Icons](https://github.com/oblador/react-native-vector-icons), [RN Gesture Handler](https://github.com/kmagiera/react-native-gesture-handler). As an example, basic Reddit App implemented in two ways: using [MobX-State-Tree](https://github.com/mobxjs/mobx-state-tree) in `/srcMobX` and using [Redux](https://github.com/reduxjs/redux) in `/srcRedux`.
 
 ### Playground