[Improvement] Tab: add title slot (#603)

docs/markdown/en-US/tab.md

@@ -105,8 +105,22 @@ In sticky mode, the tab will be fixed to top when scroll to top
 
 ```html
 <van-tabs :active="active" sticky>
-  <van-tab v-for="index in 4" :title="'选项 ' + index">
-    内容 {{ index }}
+  <van-tab v-for="index in 4" :title="'tab ' + index">
+    content {{ index }}
+  </van-tab>
+</van-tabs>
+```
+
+#### Custom title
+Use title slot to custom tab title
+
+```html
+<van-tabs :active="active">
+  <van-tab v-for="index in 2">
+    <div slot="title">
+      <van-icon name="more-o" />tab
+    </div>
+    content {{ index }}
   </van-tab>
 </van-tabs>
 ```
@@ -127,6 +141,13 @@ In sticky mode, the tab will be fixed to top when scroll to top
 | title | Tab title | `String` | - | - |
 | disabled | Whether disabled current tab | `Boolean` | `false` | - |
 
+### Tab Slot
+
+| name | Description |
+|-----------|-----------|
+| - | Content |
+| title | Custom tab |
+
 ### Tabs Event
 
 | Event | Description | Arguments |

docs/markdown/zh-CN/tab.md

@@ -111,6 +111,20 @@ export default {
 </van-tabs>
 ```
 
+#### 自定义标签
+通过 title slot 可以自定义标签内容
+
+```html
+<van-tabs :active="active">
+  <van-tab v-for="index in 2">
+    <div slot="title">
+      <van-icon name="more-o" />选项
+    </div>
+    内容 {{ index }}
+  </van-tab>
+</van-tabs>
+```
+
 ### Tabs API
 
 | 参数 | 说明 | 类型 | 默认值 | 可选 |
@@ -128,6 +142,13 @@ export default {
 | title | tab的标题 | `String` | - | - |
 | disabled | 是否禁用这个tab | `Boolean` | `false` | - |
 
+### Tab Slot
+
+| 名称 | 说明 |
+|-----------|-----------|
+| - | 标签页内容 |
+| title | 自定义标签 |
+
 ### Tabs Event
 
 | 事件名 | 说明 | 参数 |