docs: add OpenSSF Best Practices registration badge

Author: hyperpolymath

README.adoc

@@ -1,4 +1,8 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 = Game Server Admin (GSA)
+image:https://img.shields.io/badge/OpenSSF-Best_Practices-green?logo=openssourcesecurity[OpenSSF Best Practices,link="https://www.bestpractices.dev/en/projects/new?repo_url=https://github.com/hyperpolymath/game-server-admin"]
+
 :toc: preamble
 :icons: font
 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
@@ -174,6 +178,6 @@ The configuration file (`user-config.ncl`) is **gitignored** to ensure your serv
 
 == License
 
-SPDX-License-Identifier: AGPL-3.0-or-later
+SPDX-License-Identifier: MPL-2.0
 
 Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>