doc(README): fix usage docs

Author: Walker Leite

README.md

@@ -8,7 +8,8 @@ A Vue project template with [Loopback](http://loopback.io/) framework featuring
 ## Usage
 
 ```
-  $ vue-cli init InCuca/vue-loopback project-name
+  $ npm install -g vue-cli
+  $ vue init InCuca/vue-loopback project-name
   $ npm install
 ```