Add Nix to doom config

doom/init.el

@@ -128,7 +128,7 @@
        ;;lua               ; one-based indices? one-based indices
        markdown          ; writing docs for people to ignore
        ;;nim               ; python + lisp at the speed of c
-       ;;nix               ; I hereby declare "nix geht mehr!"
+       nix               ; I hereby declare "nix geht mehr!"
        ;;ocaml             ; an objective camel
        (org              ; organize your plain life in plain text
         +dragndrop       ; drag & drop files/images into org buffers