fix(create-app): should set name in docs

packages/create-vant-cli-app/generators/templates/docs/quickstart.md

@@ -4,8 +4,8 @@
 
 ```bash
 # 通过 npm 安装
-npm i vant -S
+npm i <%= name %> -S
 
 # 通过 yarn 安装
-yarn add vant
+yarn add <%= name %>
 ```

packages/create-vant-cli-app/generators/templates/src/demo-button/README.md

@@ -1,16 +1,16 @@
-# MyButton 按钮
+# DemoButton 按钮
 
 ### 介绍
 
-MyButton 是一个示例按钮组件
+DemoButton 是一个示例按钮组件
 
 ### 引入
 
 ``` javascript
 import Vue from 'vue';
-import { MyButton } from 'demo-ui';
+import { DemoButton } from '<%= name %>';
 
-Vue.use(MyButton);
+Vue.use(DemoButton);
 ```
 
 ## 代码演示