docs: add Options API and Composition API

Author: hunterliu1003

docs/content/en/index.md

@@ -192,8 +192,22 @@ Changes API name from "$vfm" to any other string value. It is useful when you us
 
 ## **API**
 
+- In Options API:
+
 Plugin API can be called within any component through `this.$vfm`.
 
+- In Composition API:
+
+```js
+import { inject } from 'vue'
+
+export default {
+  setup() {
+    const $vfm = inject('$vfm')
+  }
+}
+```
+
 ### `$vfm.show(name, params)`
 
 - Type: `Function`