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

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

docs/howto-server-delegation.md

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 # Server Delegation
 
 By default, this playbook sets up services on your Matrix server (`matrix.example.com`). To have this server officially be responsible for Matrix services for the base domain (`example.com`), you need to set up server delegation / redirection.