lock-fancy-rapid: add meta.mainProgram

Author: msanft

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

@@ -33,6 +33,7 @@ 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;
   };