feat: enable flakes and use swap

hosts/karasumaru/configuration.nix

@@ -37,6 +37,8 @@ in {
     };
   };
 
+  nix.settings.experimental-features = ["nix-command" "flakes"];
+
   virtualisation.docker.enable = true;
   virtualisation.oci-containers = {
     backend = "docker";

hosts/karasumaru/hardware-configuration.nix

@@ -28,7 +28,12 @@
     options = ["fmask=0022" "dmask=0022"];
   };
 
-  swapDevices = [];
+  swapDevices = [
+    {
+      device = "/var/lib/swapfile";
+      size = 2 * 1024; # swap size is in mb
+    }
+  ];
 
   # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
   # (the default) this is the recommended approach. When using systemd-networkd it's