Add NixOS module

This module adds the necessary configuration for hosting Financier with
nginx.

module.nix

@@ -0,0 +1,32 @@
+{ config, lib, pkgs, system, ... }:
+with lib;
+let
+  cfg = config.services.financier;
+  financier-dist = import ./dist.nix { inherit pkgs system; };
+in
+{
+  imports = [];
+
+  options.services.financier = {
+    enable = mkEnableOption "Financier";
+
+    hostName = mkOption {
+      type = types.str;
+      description = ''
+        Name for the nginx virtual host.
+      '';
+      example = "example.org";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = [ 80 443 ];
+
+    services.nginx.virtualHosts."${cfg.hostName}" = {
+      forceSSL = true;
+      enableACME = true;
+      root = financier-dist;
+      locations."/".tryFiles = "$uri $uri/ /index.html";
+    };
+  };
+}