Polish i18n (#275)

* Add Polish translation

* Add Piotr Orzechowski to contributor list

* Add unit to reading time in Polish translation

CONTRIBUTORS.md

@@ -58,4 +58,5 @@
 - [FIGBERT](https://figbert.com/)
 - [Yash Mehrotra](https://yashmehrotra.com)
 - [Paolo Mainardi](https://paolomainardi.com)
-- [Ka-Wai Lin](https://github.com/kwlin)
+- [Ka-Wai Lin](https://github.com/kwlin)
+- [Piotr Orzechowski](https://orzechowski.tech)

i18n/pl.toml

@@ -0,0 +1,23 @@
+[category]
+other = "kategoria"
+
+[tag]
+other = "tag"
+
+[series]
+other = "seria"
+
+[reading_time]
+other = "czas czytania: {{ .Count }} min"
+
+[page_not_found]
+other = "Nie znaleziono strony"
+
+[page_does_not_exist]
+other = "Wybacz, ta strona nie istnieje."
+
+[head_back]
+other = "Możesz wrócić na <a href=\"{{ . }}\">stronę domową</a>."
+
+[powered_by]
+other = "Napędzane przez"