update readme to use new vue-cli

Author: yyx990803

README.md

@@ -9,11 +9,10 @@
 The best way to get started is with [vue-cli](https://github.com/vuejs/vue-cli):
 
 ``` js
-npm install -g vue-cli
-vue init webpack-simple hello
+npm install -g @vue/cli
+vue create hello
 cd hello
-npm install
-npm run dev
+npm run serve
 ```
 
 This will setup a basic Webpack + `vue-loader` project for you, with `*.vue` files and hot-reloading working out of the box!