[Doc] add explanation of Filed native propterties (#384)

docs/markdown/en-US/field.md

@@ -77,6 +77,7 @@ Textarea Filed can be auto resize when has `autosize` prop
 ```
 
 ### API
+Filed support all native properties of input tag，such as `maxlength`、`placeholder`、`readonly`
 
 | Attribute | Description | Type | Default | Accepted Values |
 |-----------|-----------|-----------|-------------|-------------|

docs/markdown/zh-CN/field.md

@@ -79,6 +79,7 @@ Vue.component(Field.name, Field);
 ```
 
 ### API
+Filed 默认支持 Input 标签所有的原生属性，比如 `maxlength`、`placeholder`、`readonly` 等
 
 | 参数 | 说明 | 类型 | 默认值 | 可选值 |
 |-----------|-----------|-----------|-------------|-------------|