Add copyright header to docs/configuring-playbook-nginx.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-nginx.md

@@ -1,3 +1,14 @@
+<!--
+SPDX-FileCopyrightText: 2019 - 2020 MDAD project contributors
+SPDX-FileCopyrightText: 2019 - 2024 Slavi Pantaleev
+SPDX-FileCopyrightText: 2019 Paul Tötterman
+SPDX-FileCopyrightText: 2020 - 2021 Agustin Ferrario
+SPDX-FileCopyrightText: 2021 Aaron Raimist
+SPDX-FileCopyrightText: 2021 Stuart Thomson
+
+SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+
 # Configure Nginx (optional, advanced)
 
 Since 2024-01, this playbook no longer uses nginx as its reverse-proxy.