installation/download-mastofe-build.sh: Add copyright header

[ci skip]

installation/download-mastofe-build.sh

@@ -1,4 +1,7 @@
 #!/bin/sh
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
 project_id="74"
 project_branch="rebase/glitch-soc"
 static_dir="instance/static"