Add cachix, proper buildMachines config

modules/desktop/default.nix

@@ -43,6 +43,7 @@
   environment.systemPackages = with pkgs; [
     android-tools
     bottom
+    cachix
     firefox
     git
     htop

modules/shared/default.nix

@@ -13,8 +13,20 @@
     };
   };
 
+  nix.buildMachines = [{
+    hostName = "192.168.5.10";
+    systems = [ "aarch64-linux" "x86_64-linux" ];
+    protocol = "ssh";
+    sshUser = "builder";
+    sshKey = "${config.sops.secrets.builderKey.path}";
+    maxJobs = 12;
+    speedFactor = 2;
+    supportedFeatures = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+    mandatoryFeatures = [ ];
+  }];
+  nix.distributedBuilds = true;
+
   nix.extraOptions = ''
-    builders = ssh://builder@192.168.5.10?ssh-key=${config.sops.secrets.builderKey.path}
     builders-use-substitutes = false
   '';
 }