add CDN installation

Author: kevinongko

README.md

@@ -22,7 +22,8 @@ $ npm install vue-numeric --save
 ### Install as Component
 ```js
 import Vue from 'vue'
-  
+import VueNumeric from 'vue-numeric
+
 export default {
   name: 'App',
 
@@ -36,10 +37,20 @@ export default {
 ```js
 import Vue from 'vue'
 import VueNumeric from 'vue-numeric'
-  
+
 Vue.use(VueNumeric)
 ```
 
+### Install via CDN
+```html
+<script src="https://unpkg.com/vue"></script>
+<script src="https://unpkg.com/vue-numeric"></script>
+
+<script>
+  Vue.use(VueNumeric.default)
+</script>
+```
+
 ## Usage
 
 ![screen shot 2016-12-08 at 2 19 31 pm](https://cloud.githubusercontent.com/assets/15880638/21001265/f2322438-bd51-11e6-8985-f31a45702484.png)