nero: add support for distributed builds to vergil

hosts/nero/configuration.nix

@@ -125,6 +125,31 @@ in
     };
   };
 
+  nix = {
+    distributedBuilds = true;
+    settings.builders-use-substitutes = true;
+
+    buildMachines = [
+      {
+        hostName = "vergil.cfl.rr.com";
+        sshUser = "remotebuild";
+        sshKey = "/root/.ssh/id_rsa";
+        system = pkgs.stdenv.hostPlatform.system;
+        protocol = "ssh-ng";
+        maxJobs = 24;
+        speedFactor = 2;
+        mandatoryFeatures = [ ];
+
+        supportedFeatures = [
+          "nixos-test"
+          "benchmark"
+          "big-parallel"
+          "kvm"
+        ];
+      }
+    ];
+  };
+
   environment = {
     sessionVariables = {
       AVALONIA_SCREEN_SCALE_FACTORS = "HDMI-A-1=2.0;DP-1=2.0;DP-2=2.0;DP-3=2.0";