Check if the nix package has been installed

ci-helpers/check-installation-nix.sh

@@ -2,6 +2,14 @@ set -o errexit
 set -o nounset
 set -o pipefail
 
+# Check if the package was installed
+if nix-env -q razer-laptop-control; then
+  echo "razer-laptop-control package installed"
+else
+  echo "razer-laptop-control package not installed"
+  exit 1
+fi
+
 # Aparently the service is not enabled by default
 # printf "Checking that the service is enabled: "
 # systemctl --user is-enabled razercontrol.service