system: packages+services: Add nix.

system/config.scm

@@ -33,6 +33,7 @@
  dns
  linux
  networking
+ nix
  pm
  security-token
  sound
@@ -151,6 +152,7 @@
     desec-certbot-hook
     flatpak
     network-manager-applet
+    nix
     st-custom
     stumpwm
     `(,stumpwm "lib")
@@ -216,6 +218,9 @@
     (service tor-service-type)
     (service usb-modeswitch-service-type)
     (service wpa-supplicant-service-type))
+   ;; Operation
+   (list
+    (service nix-service-type))
    ;; Power
    (list
     (service thermald-service-type