feat: Add isWXAppInstalled props.

example/App.js

@@ -1,22 +1,14 @@
-/**
- * Sample React Native App
- *
- * adapted from App.js generated by the following command:
- *
- * react-native init example
- *
- * https://github.com/facebook/react-native
- */
-
 import React, { Component } from 'react';
 import { Platform, SafeAreaView, StyleSheet, Text, View } from 'react-native';
-import RNWechat from '@uiw/react-native-wechat';
+import Wechat from '@uiw/react-native-wechat';
 
 export default class App extends Component {
   state = {
     message: '--'
   };
-  componentDidMount() {
+  async componentDidMount() {
+    const isInstall = await Wechat.isWXAppInstalled();
+    console.log(':isInstall:', isInstall);
     // RNWechat.sampleMethod('Testing', 123, (message) => {
     //   this.setState({
     //     message