Update docs/configuring-playbook.md: add a copyright header

Those authors were picked up based on the current status (dae0f44603), the others (around 30 people whose contributions have been removed) being grouped as "MDAD project contributors".

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

docs/configuring-playbook.md

@@ -1,3 +1,19 @@
+<!--
+SPDX-FileCopyrightText: 2018 - 2025 Slavi Pantaleev
+SPDX-FileCopyrightText: 2018 - 2024 MDAD project contributors
+SPDX-FileCopyrightText: 2020 Sabine Laszakovits
+SPDX-FileCopyrightText: 2021 Cody Neiman
+SPDX-FileCopyrightText: 2021 Matthew Cengia
+SPDX-FileCopyrightText: 2021 Toni Spets
+SPDX-FileCopyrightText: 2022 Julian Foad
+SPDX-FileCopyrightText: 2022 Julian-Samuel Gebühr
+SPDX-FileCopyrightText: 2022 Vladimir Panteleev
+SPDX-FileCopyrightText: 2023 Shreyas Ajjarapu
+SPDX-FileCopyrightText: 2024 - 2025 Suguru Hirahara
+
+SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+
 # Configuring the playbook
 
 <sup>[Prerequisites](prerequisites.md) > [Configuring your DNS settings](configuring-dns.md) > [Getting the playbook](getting-the-playbook.md) > Configuring the playbook > [Installing](installing.md)</sup>