home: create 'modules/home' folder

Consolidating all modules under the same path, to clear out the
top-level directory.

modules/home/calibre/default.nix

@@ -0,0 +1,15 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.my.home.calibre;
+in
+{
+  options.my.home.calibre = with lib; {
+    enable = mkEnableOption "calibre configuration";
+  };
+
+  config = lib.mkIf cfg.enable {
+    home.packages = with pkgs; [
+      calibre
+    ];
+  };
+}