docs: add before-preview-change prop

Author: code-farmer-i

docs/api.md

@@ -161,6 +161,14 @@ Disabled menu. default is the upload local image menu under the image toolbar. E
 - type：`Object`
 - default：`{ accept: 'image/*' }`
 
+### before-preview-change
+
+-Type: `Function`
+-Default value: `-`
+-Callback parameters: `(text, next)`
+
+Function triggered before preview parsing. After configuring this property, you must call the next method and pass in the md text that needs to be rendered, otherwise the preview component will not be rendered.
+
 ### codemirror-config
 
 - type：`Object`

docs/zh/api.md

@@ -186,6 +186,14 @@ export default {
 
 上传本地图片的相关配置。参考高级用法：[如何插入本地图片](./senior/upload-image.md)
 
+### before-preview-change
+
+- 类型：`Function`
+- 默认值：`-`
+- 回调参数：`(text, next)`
+
+在预览解析前触发的函数，配置此属性后必须要调用 next 方法并传入需要渲染的 md 文本，否则 preview 组件将不会进行渲染。
+
 ### codemirror-config
 
 - 类型：`Object`