Merge pull request #9542 from eltociear/add-ja-doc

docs: add Japanese README

Author: zhangdaiscott

README.en-US.md

@@ -1,4 +1,4 @@
-[中文](./README.md) | English
+[中文](./README.md) | English | [日本語](./README.ja-JP.md)
 
 ![JEECG](https://jeecgos.oss-cn-beijing.aliyuncs.com/files/logov3.png "JeecgBoot低代码开发平台")
 
@@ -456,4 +456,4 @@ AI Chat Assistant
 
 If so, buy the author a cup of coffee ☺
 
-![](https://static.oschina.net/uploads/img/201903/08155608_0EFX.png)
+![](https://static.oschina.net/uploads/img/201903/08155608_0EFX.png)