docs: update vite init command (vuejs#4176) [ci skip]

Author: Otto

README.md

@@ -9,11 +9,12 @@ This is the repository for Vue 3.0.
 - Scaffold via [Vite](https://github.com/vitejs/vite):
 
   ```bash
-  # npm
-  npm init @vitejs/app
+  # npm 6.x
+  npm init vite@latest my-vue-app --template vue
+  # npm 7+, extra double-dash is needed:
+  npm init vite@latest my-vue-app -- --template vue
   # yarn
-  yarn create @vitejs/app
-  # select vue template
+  yarn create vite my-vue-app --template vue
   ```
 
 - Scaffold via [vue-cli](https://cli.vuejs.org/):