diff --git a/flake.nix b/flake.nix
index 65698764..0da6152c 100644
--- a/flake.nix
+++ b/flake.nix
@@ -95,6 +95,8 @@
         }
       );
 
+      # CORIOLIS_TOP must be set before execution
+      # example: CORIOLIS_TOP="$(mktemp -d)" && ./result/bin/cgt
       defaultPackage = forAllSystems (system: self.packages.${system}.unicorn);
 
       devShell = forAllSystems (system: