Fix ExecStart in Bookwyrm systemd unit

nixos-module.nix

@@ -1,11 +1,12 @@
 { pkgs , ... } :
 
+with pkgs ;
+with pkgs . kernelmaft ;
+
 {
 	nixpkgs = {
 		overlays = [
 			( self : super :
-				with pkgs ;
-
 				{
 					kernelmaft = {
 
@@ -54,13 +55,13 @@
 
 	systemd = {
 		units = {
-			bookwyrm = {
+			"bookwyrm.service" = {
 				text = ''
 					[Unit]
 					After=network.target
 
 					[Service]
-					ExecStart=$out/bin/bookwyrm
+					ExecStart=${bookwyrm}/bin/bookwyrm
 					WorkingDirectory=/var/lib/bookwyrm
 				'' ;
 			} ;