chore: add heading

Author: yuyinws

packages/docs/guide/index.md

@@ -22,6 +22,8 @@ To introduce some of the main ideas, we're going to consider this example:
 
 Let's start by looking at the root component, `App.vue`.
 
+### App.vue
+
 ```vue [App.vue]
 <template>
  <h1>Hello App!</h1>

packages/docs/zh/guide/index.md

@@ -24,6 +24,7 @@ Vue Router 基于 Vue 的组件系统构建，你可以通过配置**路由**来
 
 让我们首先来看根组件, `App.vue`。
 
+### App.vue
 ```vue [App.vue]
 <template>
  <h1>Hello App!</h1>