Add German language repo to MIRRORS.md

Added [German repo](https://github.com/arentro/degoogle_german) thanks to arentro!

MIRRORS.md

@@ -14,4 +14,8 @@ Official mirrors are the main sources and are maintained by me (@tycrek). Commun
 
 - [GitLab mirror](https://gitlab.com/SheepKid12/degoogle) from u/SheepKid12
 - [Gitea mirror](https://git.xerbo.net/Xerbo/degoogle) from [@Xerbo](https://github.com/Xerbo)
-- [BookRefine Publishing](https://bookrefine.com/degoogle/) (thanks @GreyLivesMatter for the updated link)
+- [BookRefine Publishing](https://bookrefine.com/degoogle/) (thanks @GreyLivesMatter for the updated link)
+
+## Non-english mirrors
+
+- [German/Deutsch](https://github.com/arentro/degoogle_german) from [@arentro](https://github.com/arentro)