Add copyright header to docs/configuring-playbook-ssl-certificates.md

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

docs/configuring-playbook-ssl-certificates.md

@@ -1,3 +1,14 @@
+<!--
+SPDX-FileCopyrightText: 2018 - 2024 Slavi Pantaleev
+SPDX-FileCopyrightText: 2020 - 2024 MDAD project contributors
+SPDX-FileCopyrightText: 2020 Aaron Raimist
+SPDX-FileCopyrightText: 2022 Alejo Diaz
+SPDX-FileCopyrightText: 2022 Julian Foad
+SPDX-FileCopyrightText: 2024 - 2025 Suguru Hirahara
+
+SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+
 # Adjusting SSL certificate retrieval (optional, advanced)
 
 By default, this playbook retrieves and auto-renews free SSL certificates from [Let's Encrypt](https://letsencrypt.org/) for the domains it needs (e.g. `matrix.example.com` and others)