Created by: kowalczewski
There are two commits in this pull request: 1) I included my name in Contributors.md file; 2) I suggested changes in the Polish translation of README file: Polish "kontrybucja" is a naive translation of English "contribution", but this word doesn't exist in Polish in this context (PL dictionary: https://sjp.pwn.pl/szukaj/kontrybucja.html). Therefore, I replaced "kontrybucja" with "wkład".