Update security readme.

Author: christophstrobl

SECURITY.adoc

@@ -1,9 +1,16 @@
-# Security Policy
+= Security Policy
 
-## Supported Versions
+== Reporting a Vulnerability
 
-Please see the https://spring.io/projects/spring-data-mongodb[Spring Data MongoDB] project page for supported versions.
+Please, https://github.com/spring-projects/security-advisories/security/advisories/new[open a draft security advisory] if you need to disclose and discuss a security issue in private with the Spring Data team.
+Note that we only accept reports against https://spring.io/projects/spring-data#support[supported versions].
 
-## Reporting a Vulnerability
+For more details, check out our https://spring.io/security-policy[security policy].
+
+== JAR signing
+
+Spring Data JARs released on Maven Central are signed.
+You'll find more information about the key here: https://spring.io/GPG-KEY-spring.txt
+
+Versions released prior to 2023 may be signed with a different key.
 
-Please don't raise security vulnerabilities here. Head over to https://pivotal.io/security to learn how to disclose them responsibly.