add how to upgrade RN

Author: Uncle Charlie

README.md

@@ -1,3 +1,53 @@
 # react-native-tutorial
 
 This is a react native tutorial demos repo.
+
+## How to upgrade to the latest RN
+
+I think the best way to do this is to create a new RN project that has the same name as your existing project.
+
+Then there are two parts you will have to deal with.
+1. `package.json` file related.
+2. non-`package.json` file related.
+
+### `Package.json` things
+
+Copy newest dependencies and replace your existing ones and keep others.
+
+Basically these stuff.
+```json
+  "dependencies": {
+    "react": "16.6.3",
+    "react-native": "0.58.3"
+  },
+  "devDependencies": {
+    "babel-core": "^7.0.0-bridge.0",
+    "babel-jest": "24.0.0",
+    "jest": "24.0.0",
+    "metro-react-native-babel-preset": "0.51.1",
+    "react-test-renderer": "16.6.3"
+  },
+  "jest": {
+    "preset": "react-native"
+  }
+```
+
+### Non-`package.json` things
+If your package is really old that you still have `index.ios.js` / `index.android.js`. You will have to do something to your codes to morden styles, like there might have `App.js` and `app.json` and `index.js`. Generally files like this.
+
+Then copy files like:
+* `.buckconfig`
+* `.flowconfig`
+* `.gitattributes`
+* `.gitignore`, **DO REMEMBER** to merge this file, you have to keep you own modification.
+* `.watchmanconfig`
+
+### Upgrade iOS
+
+You might going to upgrade swift version. Follow the swift way. I met some problems in swift 4.2. The class method can not be called in OC. As there's a modification in Swift 4.2.
+
+### Upgrade Android
+
+Just open your Android Studio and let the IDE do the upgrade job.
+
+If you used NDK, well downlad a new version which is specified in RN doc.