diff --git a/NixOS.md b/NixOS.md
index 5a1ade8..848a86a 100644
--- a/NixOS.md
+++ b/NixOS.md
@@ -25,6 +25,7 @@ This document contains general notes about NixOS that are independent of my NixO
   * [Evaluate expressions](#evaluate-expressions)
   * [Escape strings](#escape-strings)
   * [Run AppImages](#run-appimages)
+  * [Graphic drivers](#graphic-drivers)
   * [Additional resources](#additional-resources)
     * [Nix Pills](#nix-pills)
     * [Papers](#papers)
diff --git a/examples/systemd-timer.nix b/examples/systemd-timer.nix
index d0466c9..9de234e 100644
--- a/examples/systemd-timer.nix
+++ b/examples/systemd-timer.nix
@@ -73,7 +73,9 @@
     before = [ "shutdown.target" "sleep.target" ];
 
     # https://man.archlinux.org/man/systemd.service.5.en#OPTIONS
-    #   More options e.g.: https://man.archlinux.org/man/systemd.exec.5.en#SCHEDULING
+    #   More options are documented e.g. here:
+    #     https://man.archlinux.org/man/systemd.exec.5.en#SCHEDULING
+    #     https://man.archlinux.org/man/systemd.exec.5.en#USER/GROUP_IDENTITY
     #
     # Example: https://github.com/NixOS/nixpkgs/blob/e9b4b56e5a20ac322c0c01ccab7ec697ab076ea0/nixos/modules/tasks/filesystems/btrfs.nix#L132-L142
     serviceConfig = {