docs(message): add use not int setup demo (#215)

* docs(message): use message outside of setup

* docs(message): use html

* Apply suggestions from code review

* docs(message): put use message outside setup to Q&A section

* Apply suggestions from code review

Co-authored-by: tusimple <jiwen.bai@tusimple.ai>
Co-authored-by: 07akioni <07akioni2@gmail.com>

src/message/demos/enUS/index.demo-entry.md

@@ -94,3 +94,47 @@ multiple-line
 | Name    | Type | Description |
 | ------- | ---- | ----------- |
 | destroy | `()` |             |
+
+## Q & A
+
+### Use Message Outside Setup
+
+<n-space vertical>
+<n-alert type="warning">
+  You need to mount the return value of <n-text code>useMessage</n-text> to the window in the top-level setup and then call it. Before calling it, you need to make sure that message has been mounted successfully.
+</n-alert>
+
+```html
+<!-- App.vue -->
+<n-message-provider>
+  <content />
+</n-message-provider>
+```
+
+```html
+<!-- content.vue -->
+<template>...</template>
+
+<script>
+  import { useMessage } from 'naive-ui'
+
+  // content
+  export default {
+    setup() {
+      window.$message = useMessage()
+    }
+  }
+</script>
+```
+
+```js
+// xxx.js
+export const handler = () => {
+  // You need to ensure that window.$message = message has been executed in setup
+  window.$message.success(
+    'Cause you walked hand in hand With another man in my place'
+  )
+}
+```
+
+</n-space>

src/message/demos/zhCN/index.demo-entry.md

@@ -94,3 +94,47 @@ multiple-line
 | 名称    | 类型 | 说明 |
 | ------- | ---- | ---- |
 | destroy | `()` |      |
+
+## Q & A
+
+### 在 setup 外使用
+
+<n-space vertical>
+<n-alert type="warning">
+  如果你想在 setup 外使用信息，你需要在顶层 setup 中把 <n-text code>useMessage</n-text> 返回的 message 值挂载到 window 下然后再调用，调用前需要确保 message 已经挂载成功。
+</n-alert>
+
+```html
+<!-- App.vue -->
+<n-message-provider>
+  <content />
+</n-message-provider>
+```
+
+```html
+<!-- content.vue -->
+<template>...</template>
+
+<script>
+  import { useMessage } from 'naive-ui'
+
+  // content
+  export default {
+    setup() {
+      window.$message = useMessage()
+    }
+  }
+</script>
+```
+
+```js
+// xxx.js
+export const handler = () => {
+  // 需要确保已经在 setup 中执行了 window.$message = message
+  window.$message.success(
+    'Cause you walked hand in hand With another man in my place'
+  )
+}
+```
+
+</n-space>