Add README in Japanese

README.md

@@ -30,7 +30,7 @@ To check out docs, visit [nginxui.com](https://nginxui.com).
 
 [![Stargazers over time](https://starchart.cc/0xJacky/nginx-ui.svg)](https://starchart.cc/0xJacky/nginx-ui)
 
-English | [Español](README-es.md) | [简体中文](README-zh_CN.md) | [繁體中文](README-zh_TW.md) | [Tiếng Việt](README-vi_VN.md)
+English | [Español](README-es.md) | [简体中文](README-zh_CN.md) | [繁體中文](README-zh_TW.md) | [Tiếng Việt](README-vi_VN.md) | [日本語](README-ja_JP.md)
 
 <details>
   <summary>Table of Contents</summary>