Add Polish tutorial link to README

Author: C4illin

README.md

@@ -128,6 +128,8 @@ Tutorial in french: <https://belginux.com/installer-convertx-avec-docker/>
 
 Tutorial in chinese: <https://xzllll.com/24092901/>
 
+Tutorial in polish: <https://kreatywnyprogramista.pl/convertx-lokalny-konwerter-plikow>
+
 ## Screenshots
 
 ![ConvertX Preview](images/preview.png)