re-organize configuration

poseidon.nix

@@ -0,0 +1,25 @@
+{ ... }:
+
+{
+  imports = [
+    # Default configuration
+    ./base
+
+    # Service definitions
+    ./services
+
+    # Configuration secrets
+    ./secrets
+
+    # Host-specific config
+    ./hosts/poseidon
+  ];
+
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It‘s perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.stateVersion = "20.09"; # Did you read the comment?
+}