added remote build user in box

hosts/box/default.nix

@@ -10,6 +10,7 @@
     ./glance.nix
     ./packages.nix
     ./hardware-configuration.nix
+    ./remotebuild_user.nix
     ../../modules/common/nix.nix
     ../../modules/raspberrypi.nix
     ../../modules/common/networking.nix

hosts/box/remotebuild_user.nix

@@ -0,0 +1,17 @@
+{ config, pkgs, ... }:
+
+{
+  nix.buildMachines = [ {
+    hostName = "builder";
+    system = "x86_64-linux";
+    protocol = "ssh-ng";
+    maxJobs = 1;
+    speedFactor = 2;
+    supportedFeatures = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+    mandatoryFeatues = [ ];
+    } ];
+    nix.distributedBuilds = true;
+    nix.extraOptions = ''
+      builders-use-substitutes = true
+      '';
+}