Add missing configuration to .env.tpl

.env.tpl

@@ -45,6 +45,8 @@ NOPAQUE_ADMIN=
 NOPAQUE_CONTACT=
 # Example: nopaque.localhost
 NOPAQUE_DOMAIN=
+# Choose one: False, True
+NOPAQUE_EXECUTE_NOTIFICATIONS=
 # Choose one: CRITICAL, ERROR, WARNING, INFO, DEBUG
 NOPAQUE_LOG_LEVEL=
 # Example: nopaque Admin <nopaque@example.com>