Add header for exclusive CD (#3852)

README.md

@@ -109,6 +109,8 @@ Additionally, the users listed in this repository still serve as the contacts fo
 For that reason, CD permissions are also only granted to components with at least one maintainer.
 In particular, the Jenkins security team will _not_ make an effort to reach out to GitHub committers when maintainers (and security contacts, see below) are unresponsive before [announcing vulnerabilities without a fix](https://www.jenkins.io/security/plugins/#unresolved).
 
+### Exclusively using JEP-229 CD
+
 It is also possible to enable JEP-229 CD exclusively, i.e., the listed users will not be able to create new releases, but remain contacts for security issues and plugin/component governance questions. 
 
 ```yaml