update document.md

Author: xiajianjun

document.md

@@ -183,12 +183,10 @@ validator | description | rule example
 `url`   | validate url | ....
 `email` | validate email | ....
 `ip`    | validate ip | ....
-`required`  | validate required | ....
+`required`  | validate required | `['tagId,userId', 'required' ]`
 `length`    | validate length | ....
-`minLength` | validate minLength | ....
-`maxLength` | validate maxLength | ....
-`size`  | validate size | ....
-`min`   | validate min | ....
+`size`  | validate size | `['tagId', 'size', 'min'=>4, 'max'=>567]`
+`min`   | validate min | `['title', 'min', 'min' => 40],`
 `max`   | validate max | ....
 `in`    | validate in | ....
 `string`    | validate string | ....