add link to ru readme

Author: Blueberryy

README_ru.md

@@ -12,6 +12,7 @@
 ---
 <p align="center">
   <a href="README.md">English</a> -
+  <a href="README_ru.md">Русский</a> -
   <a href="README_cn.md">简体中文</a>
 </p>
 &nbsp;