chore: add docs

Author: chrisbing

README.md

@@ -1,2 +1,134 @@
 # vue-function-api-extra
-Providing plugin and helper functions for vue-function-api, so that we can use vue-route, vuex, mixins, prototype helpers ...
+
+Providing plugin and helper functions for [vue-function-api](https://github.com/vuejs/vue-function-api), so that we can use vue-route, vuex, helpers in prototype ...
+
+```js
+
+import { useGetters } from 'vue-function-api-extra'
+import {
+    value,
+} from 'vue-function-api'
+
+export default {
+    setup(props, context){
+        
+        const getters = useGetters(context, ['userInfo', 'otherGetter'])
+        
+        // use route
+        const route = context.route
+        const id = value(route.params.id)
+        const goBack = () => {
+            context.router.goBack()
+        }
+        
+        // use store
+        const store = context.store
+        
+        // use properties
+        // if you run "Vue.prototype.$isAndroid = true" before
+        const isAndroid = context.isAndroid
+        
+        
+        return {
+            ...getters,
+            id,
+            goBack,
+        }
+    }
+    
+}
+
+```
+
+# install
+
+```
+yarn add vue-function-api-extra
+```
+
+or
+
+```
+npm install vue-function-api-extra --save
+```
+
+# Install Plugin
+
+First you should install the plugins.
+
+**Notice: You should install the plugin before other plugins installed**
+
+```js
+
+import Vue from 'vue'
+import { plugin } from 'vue-function-api-extra'
+
+Vue.use(plugin)
+
+// use other plugins
+
+```
+
+# Use properties in context
+
+```js
+export default {
+    setup(props, context){
+        
+        // use route
+        const route = context.route
+        
+        // use store
+        const store = context.store
+        
+        // use properties
+        // if you run "Vue.prototype.$isAndroid = true" before
+        const isAndroid = context.isAndroid
+        
+        return {
+            ...getters
+        }
+    }
+    
+}
+```
+
+
+# Helpers
+
+## useGetters
+
+### description
+ 
+use Getters in Vuex
+
+### params
+
+#### context
+
+**description:** Setup Context in ```vue-function-api``` 
+**type:** SetupContext
+
+
+#### getters
+
+**description** names of getters
+**type:** string[]
+
+### example
+
+```js
+import { useGetters } from 'vue-function-api-extra'
+
+export default {
+    setup(props, context){
+        
+        const getters = useGetters(context, ['userInfo', 'otherGetter'])
+
+        return {
+            ...getters
+        }
+    }
+    
+}
+```