chore(ops/terraform): add license information

This is the result of a `"reuse annotate --copyright "The TVL Authors"
--license MIT"` in that directory, making it conformant with the REUSE
Specification:

https://reuse.software/spec

Change-Id: I13e069b4621e8d5ccb7a09c12f772d70dea40a11
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10170
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

ops/terraform/deploy-nixos/nixos-copy.sh

@@ -1,4 +1,9 @@
 #!/usr/bin/env bash
+
+# SPDX-FileCopyrightText: 2023 The TVL Authors
+#
+# SPDX-License-Identifier: MIT
+
 #
 # Copies a NixOS system to a target host, using the provided key,
 # or whatever ambient key is configured if the key is not set.