systemd: add user target support

This allows us to define system user targets in addition to the existing
services, timers and sockets.

Furthermore, we add a top-level configuration keyword:

 - Documentation

1 files changed, 6 insertions, 0 deletions

diff --git a/nixos/modules/system/boot/systemd-unit-options.nix b/nixos/modules/system/boot/systemd-unit-options.nix
index f4892244de4..731b1701e00 100644
--- a/nixos/modules/system/boot/systemd-unit-options.nix
+++ b/nixos/modules/system/boot/systemd-unit-options.nix
@@ -77,6 +77,12 @@ in rec {
       description = "Description of this unit used in systemd messages and progress indicators.";
     };
 
+    documentation = mkOption {
+      default = [];
+      type = types.listOf types.str;
+      description = "A list of URIs referencing documentation for this unit or its configuration.";
+    };
+
     requires = mkOption {
       default = [];
       type = types.listOf types.str;