feat: add Badge component (#7602)

src/badge/README.md

@@ -0,0 +1,77 @@
+# Badge
+
+### Install
+
+```js
+import Vue from 'vue';
+import { Badge } from 'vant';
+
+Vue.use(Badge);
+```
+
+## Usage
+
+### Basic Usage
+
+```html
+<van-badge content="5">
+  <div class="child" />
+</van-badge>
+<van-badge dot>
+  <div class="child" />
+</van-badge>
+
+<style>
+  .child {
+    width: 36px;
+    height: 36px;
+    background: #f2f3f5;
+    border-radius: 4px;
+  }
+</style>
+```
+
+### Max
+
+```html
+<van-badge content="20" max="9">
+  <div class="child" />
+</van-badge>
+<van-badge content="200" max="99">
+  <div class="child" />
+</van-badge>
+```
+
+### Custom Color
+
+```html
+<van-badge content="5" color="#1989fa">
+  <div class="child" />
+</van-badge>
+<van-badge dot color="#1989fa">
+  <div class="child" />
+</van-badge>
+```
+
+### Standaline
+
+```html
+<van-badge content="200" max="99" />
+```
+
+## API
+
+### Props
+
+| Attribute | Description | Type | Default |
+| --- | --- | --- | --- |
+| content | Badge content | _number \| string_ | - |
+| color | Background color | _string_ | `#ee0a24` |
+| dot | Whether to show dot | _boolean_ | `false` |
+| max | Max value，show `{max}+` when exceed，only works when content is number | _number \| string_ | - |
+
+### Slots
+
+| Name    | Description  |
+| ------- | ------------ |
+| default | Default slot |