[Improment] add $toast/$dialog to Vue.prototype (#363)

docs/markdown/en-US/button.md

@@ -35,8 +35,8 @@ Vue.component(Button.name, Button);
 #### Loading
 
 ```html 
-<van-button loading></van-button>
-<van-button loading type="primary"></van-button>
+<van-button loading />
+<van-button loading type="primary" />
 ```
 
 #### Custom Tag

docs/markdown/en-US/dialog.md

@@ -40,6 +40,19 @@ Used to confirm some messages, including a confirm button and a cancel button
 });
 ```
 
+#### $dialog Method
+After import the Dialog component, the $dialog method is automatically mounted on Vue.prototype, making it easy to call within a vue component.
+
+```js
+export default {
+  mounted() {
+    this.$dialog.alert({
+      message: 'Content'
+    });
+  }
+}
+```
+
 ### Methods
 
 | Name | Attribute | Return value | Description |

docs/markdown/en-US/toast.md

@@ -51,6 +51,17 @@ const timer = setInterval(() => {
 }, 1000);
 ```
 
+#### $toast Method
+After import the Toast component, the $toast method is automatically mounted on Vue.prototype, making it easy to call within a vue component.
+
+```js
+export default {
+  mounted() {
+    this.$toast('Some messages');
+  }
+}
+```
+
 ### Methods
 
 | Methods | Attribute | Return value | Description |