add link of Japanese to README

Author: masah517

README.md

@@ -8,7 +8,7 @@
   <a href="https://github.com/skydoves"><img alt="Profile" src="https://skydoves.github.io/badges/skydoves.svg"/></a>
 </p>
 <p align="center">
-<a href="/README_AR.md" target="_blank"> Arabic </a> | <a href="/README.md" target="_blank"> English </a> | <a href="/README_KR.md" target="_blank"> 한국어 </a> | <a href="/README_DE.md" target="_blank"> Deutsch </a>| <a href="/README_ES.md" target="_blank"> Español</a> | <a href="/README_TR.md" target="_blank"> Turkish</a> | <a href="/README_ID.md" target="_blank"> Bahasa Indonesia</a> | <a href="/README_FR.md" target="_blank"> Français</a> | <a href="/README_PT.md" target="_blank"> Portuguese</a> | <a href="/README_KHM.md" target="_blank">ភាសាខ្មែរ</a> | <a href="/README_VI.md" target="_blank">Vietnamese</a> | <a href="/README_CN.md" target="_blank">中文</a>
+<a href="/README_AR.md" target="_blank"> Arabic </a> | <a href="/README.md" target="_blank"> English </a> | <a href="/README_KR.md" target="_blank"> 한국어 </a> | <a href="/README_DE.md" target="_blank"> Deutsch </a>| <a href="/README_ES.md" target="_blank"> Español</a> | <a href="/README_TR.md" target="_blank"> Turkish</a> | <a href="/README_ID.md" target="_blank"> Bahasa Indonesia</a> | <a href="/README_FR.md" target="_blank"> Français</a> | <a href="/README_PT.md" target="_blank"> Portuguese</a> | <a href="/README_KHM.md" target="_blank">ភាសាខ្មែរ</a> | <a href="/README_VI.md" target="_blank">Vietnamese</a> | <a href="/README_CN.md" target="_blank">中文</a> | <a href="/README_JP.md" target="_blank">日本語</a>
 </p>