Polish README with notice of move to Spring Security 7.0

Author: jgrandja

README.adoc

@@ -1,11 +1,12 @@
 = Spring Authorization Server image:https://badges.gitter.im/Join%20Chat.svg[Gitter,link=https://gitter.im/spring-projects/spring-security?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge] image:https://github.com/spring-projects/spring-authorization-server/actions/workflows/continuous-integration-workflow.yml/badge.svg["Build Status", link="https://github.com/spring-projects/spring-authorization-server/actions/workflows/continuous-integration-workflow.yml"] image:https://img.shields.io/badge/Revved%20up%20by-Develocity-06A0CE?logo=Gradle&labelColor=02303A["Revved up by Develocity", link="https://ge.spring.io/scans?&search.rootProjectNames=spring-authorization-server"]
 
-[IMPORTANT]
-====
+== NOTICE:
+
 Spring Authorization Server has https://spring.io/blog/2025/09/11/spring-authorization-server-moving-to-spring-security-7-0[moved to Spring Security 7.0].
 
 This repository will become inactive after https://spring.io/projects/spring-authorization-server#support[OSS Support] ends for the *1.5.x* branch in June 2026.
-====
+
+'''
 
 The Spring Authorization Server project, led by the https://spring.io/projects/spring-security/[Spring Security] team, is focused on delivering https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1-07#section-1.1[OAuth 2.1 Authorization Server] support to the Spring community.