Add copyright header to docs/howto-srv-server-delegation.md

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

docs/howto-srv-server-delegation.md

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+SPDX-FileCopyrightText: 2023 - 2024 Antoine-Ali Zarrouk
+SPDX-FileCopyrightText: 2023 - 2025 Slavi Pantaleev
+SPDX-FileCopyrightText: 2024 - 2025 Suguru Hirahara
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+SPDX-License-Identifier: AGPL-3.0-or-later
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 # Server Delegation via a DNS SRV record (advanced)
 
 **Reminder** : unless you are affected by the [Downsides of well-known-based Server Delegation](howto-server-delegation.md#downsides-of-well-known-based-server-delegation), we suggest you **stay on the simple/default path**: [Server Delegation](howto-server-delegation.md) by [configuring well-known files](configuring-well-known.md) at the base domain.