[new feature] Rate: add allow-half prop (#3134)

packages/rate/en-US.md

@@ -41,18 +41,51 @@ export default {
 <van-rate
   v-model="value"
   :size="25"
-  :count="6"
-  color="#07c160"
-  void-color="#ceefe8"
+  color="#f44"
+  void-icon="star"
+  void-color="#eee"
 />
 ```
 
+#### Half Star
+
+```html
+<van-rate
+  v-model="value"
+  allow-half
+  void-icon="star"
+  void-color="#eee"
+/>
+```
+
+```javascript
+export default {
+  data() {
+    return {
+      value: 2.5
+    };
+  }
+}
+```
+
+#### Custom Count
+
+```html
+<van-rate v-model="value" :count="6" />
+```
+
 #### Disabled
 
 ```html
  <van-rate v-model="value" disabled />
 ```
 
+#### Readonly
+
+```html
+<van-rate v-model="value" readonly />
+```
+
 ### API
 
 | Attribute | Description | Type | Default |
@@ -64,6 +97,7 @@ export default {
 | void-color | Void color | `String` | `#c7c7c7` |
 | icon | Selected icon | `String` | `star` |
 | void-icon | Void icon | `String` | `star-o` |
+| allow-half | Whether to allow half star | `Boolean` | `false` |
 | readonly | Whether to be readonly | `Boolean` | `false` |
 | disabled | Whether to disable rate | `Boolean` | `false` |
 | disabled-color | Disabled color | `String` | `#bdbdbd` |