docs(nixos): clarify primary user option

configs/nixos/modules/default.nix

@@ -13,8 +13,8 @@
       type = lib.types.str;
       default = "alexion";
       description = ''
-        Primary interactive user for this system.
-        This drives the system account and Home Manager user together.
+        Names the primary user account.
+        Host configuration uses this name for the Home Manager user.
       '';
     };
   };