add description about overridden methods

Author: ValKmjolnir

doc/4_godelscript_language.en.md

@@ -686,6 +686,7 @@ schema MyFile extends File {}
 ##### Method Override
 
 If the subclass implementation contains a method with the same name as the parent class, the parent method will be **overridden** by the subclass method.
+The overridden method can use different parameter and return type. There's no need to use the same parameter and return type of parent class method.
 
 ```rust
 schema File {

doc/4_godelscript_language.md

@@ -686,6 +686,7 @@ schema MyFile extends File {}
 ##### Method Override
 
 如果子类的实现中存在与父类同名的方法，则父类的方法会被子类方法**覆盖**。
+覆盖方法的参数和返回值类型没有限制，不需要与父类保持一致。
 
 ```rust
 schema File {