Translation to Polish (trekhleb#115)

* Create README.pl-PL.md

Translation to Polish

* Update README.md

adding Polish language to the list

Author: pavelekpl

README.md

@@ -13,7 +13,8 @@ to YouTube videos).
 _Read this in other languages:_
 [简体中文](README.zh-CN.md),
 [繁體中文](README.zh-TW.md),
-[한국어](README.ko-KR.md)
+[한국어](README.ko-KR.md),
+[Polish](README.pl-PL.md)
 
 > We’re writing a book that will clearly explain, in detail, the main algorithms. 
 If you’d like to be notified when the “JavaScript Algorithms” book