📝 Add Japanese translations for README.md (#12819)

I created Japanese translated README.

Author: eltociear

README.md

@@ -25,7 +25,7 @@
 </p>
 
 <p align="center">
-<a href="README_zh_CN.md">中文</a>
+<a href="README_zh_CN.md">中文</a> | <a href="README_ja_JP.md">日本語</a>
 </p>
 
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