lock-fancy-rapid: add meta.mainProgram; format (#355172)

Author: drupol

pkgs/applications/window-managers/i3/lock-fancy-rapid.nix

@@ -1,4 +1,10 @@
-{ lib, stdenv, fetchFromGitHub, xorg, i3lock }:
+{
+  lib,
+  stdenv,
+  fetchFromGitHub,
+  xorg,
+  i3lock,
+}:
 
 stdenv.mkDerivation {
   pname = "i3lock-fancy-rapid";
@@ -33,6 +39,7 @@ stdenv.mkDerivation {
     description = "Faster implementation of i3lock-fancy";
     homepage = "https://github.com/yvbbrjdr/i3lock-fancy-rapid";
     maintainers = with maintainers; [ nickhu ];
+    mainProgram = "i3lock-fancy-rapid";
     license = licenses.bsd3;
     platforms = platforms.linux;
   };