Add polymouth

options/system/boot/default.nix

@@ -5,6 +5,7 @@
 in {
   imports = [
     ./secure-boot.nix
+    ./plymouth.nix
   ];
 
   options.myOptions.system.boot = {

options/system/boot/plymouth.nix

@@ -0,0 +1,25 @@
+{ lib, ... }: with lib; let
+  inherit (lib) mkEnableOption mkOption types;
+in
+{
+  options.myOptions.system.boot.plymouth = {
+    enable = mkEnableOption ''Plymouth boot splash.'';
+
+    withThemes = mkEnableOption ''
+      Whether or not themes from https://github.com/adi1090x/plymouth-themes
+      should be enabled and configured.
+    '';
+
+    selectedTheme = mkOption {
+      type = types.str;
+      default = "bgrt";
+      description = ''
+        Choose which theme to use.
+
+        If you have `myOptions.system.boot.plymouth.withThemes` enabled, you can use more themes from the
+        https://github.com/adi1090x/plymouth-themes project. You can find the the available theme names at
+        https://github.com/NixOS/nixpkgs/blob/master/pkgs/data/themes/adi1090x-plymouth-themes/shas.nix.
+      '';
+    };
+  };
+}