Add: DOM change detection, android setup guide on README

README.md

 `npm install react-native-autoheight-webview@0.2.3 --save` (rn < 0.44)
 
 ## android
-`react-native link react-native-autoheight-webview`
+1. `react-native link react-native-autoheight-webview`
+2. in MainApplication.java
+```javascript
+import com.dscj.autoheightwebview.AutoHeightWebViewPackage; // Add this
+
+public class MainApplication extends Application implements ReactApplication {
+  //...
+  private final ReactNativeHost mReactNativeHost = new ReactNativeHost(this) {
+    //...
+    @Override
+    protected List<ReactPackage> getPackages() {
+      return Arrays.<ReactPackage>asList(
+        //...
+        new AutoHeightWebViewPackage() // Add this
+        //...
+```
 
 ## showcase
 ![react-native-autoheight-webview ios](https://media.giphy.com/media/l4FGyhnvWfUgxCfe0/200w.gif)&nbsp;
     scalesPageToFit={Platform.OS === 'android' ? true : false}
     // baseUrl not work in android 4.3 or below version
     enableBaseUrl={true}
-    // offset of rn webview margin 
+    // offset of rn webview margin
     heightOffset={5}
     // default width is the width of screen
     // if there are some text selection issues on iOS, the width should be reduced more than 15 and the marginTop should be added more than 35

autoHeightWebView/index.android.js

 const RCTAutoHeightWebView = requireNativeComponent(
   "RCTAutoHeightWebView",
   AutoHeightWebView,
-  { nativeOnly: 
+  { nativeOnly:
     {
       nativeOnly: {
         onLoadingStart: true,
         AutoHeightWebView.onMessage = function (message) {
             AutoHeightWebView.send(String(document.body.offsetHeight));
         };
-    } ()); 
+        MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
+        var observer = new MutationObserver(function() {
+            AutoHeightWebView.send(String(document.body.offsetHeight));
+        });
+        observer.observe(document, {
+            subtree: true,
+            attributes: true
+        });
+    } ());
     `
   : `
     ; (function () {
         document.addEventListener('message', function (e) {
             window.postMessage(String(document.body.offsetHeight));
         });
-    } ()); 
+        MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
+        var observer = new MutationObserver(function() {
+            window.postMessage(String(document.body.offsetHeight));
+        });
+        observer.observe(document, {
+            subtree: true,
+            attributes: true
+        });
+    } ());
     `;

autoHeightWebView/index.ios.js

 
 const BaseScript =
     `
-    ; 
+    ;
     (function () {
         var i = 0;
         var height = 0;
         updateHeight();
         window.addEventListener('load', updateHeight);
         window.addEventListener('resize', updateHeight);
+        MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
+        var observer = new MutationObserver(updateHeight);
+        observer.observe(document, {
+            subtree: true,
+            attributes: true
+        });
     } ());
     `;
 
 const IframeBaseScript =
     `
-    ; 
+    ;
     (function () {
         var i = 0;
         var height = 0;
         updateHeight();
         window.addEventListener('load', updateHeight);
         window.addEventListener('resize', updateHeight);
+        MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
+        var observer = new MutationObserver(updateHeight);
+        observer.observe(document, {
+            subtree: true,
+            attributes: true
+        });
     } ());
-    `;
+    `;