chore: add an example for SSR (#8298)

<img width="740" alt="Screen Shot 2020-05-20 at 16 31 30" src="https://user-images.githubusercontent.com/1174278/82458770-673d8880-9ab7-11ea-81d3-8ac0c1e52705.png">

example/types/react-native-web.d.ts

@@ -0,0 +1,16 @@
+declare module 'react-native-web' {
+  export const AppRegistry: {
+    registerComponent(
+      name: string,
+      callback: () => React.ComponentType<any>
+    ): void;
+
+    getApplication(
+      name: string,
+      options?: { initialProps: object }
+    ): {
+      element: React.ReactElement;
+      getStyleElement(): React.ReactElement;
+    };
+  };
+}