Add some ram management stuff

This will:
    - Add a 1GB swap file
    - Enable zram
    - Enable early oom

hosts/modules/base.nix

@@ -11,6 +11,18 @@
     shell = pkgs.fish;
   };
 
+  # enable a 1GB swap file
+  swapDevices = [{
+    device = "/swapfile";
+    size = 1024;
+  }];
+
+  # enable zram. not totally sure if this does it in physical ram or just swap
+  zramSwap.enable = true;
+
+  # enable earlyoom to stop the system becoming unresponsive when out of ram
+  services.earlyoom.enable = true;
+
   networking.firewall.allowedTCPPorts = [ 8000 8080 ];
 
   # Set your time zone.