add nicrosil and username variable

home.nix

@@ -1,10 +1,10 @@
-{ config, pkgs, ... }:
+{ config, pkgs, username ? "abby", ... }:
 
 {
   # Home Manager needs a bit of information about you and the
   # paths it should manage.
-  home.username = "abby";
-  home.homeDirectory = "/home/abby";
+  home.username = username;
+  home.homeDirectory = "/home/${username}";
 
   # This value determines the Home Manager release that your
   # configuration is compatible with. This helps avoid breakage