docs(changelog): Clarify 5.0.0

Author: epage

CHANGELOG.md

@@ -4,7 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
-## 5.0.0 - 2022-11-24
+## 5.0.0 - TBD
+
+*available through `unstable-v5` feature flag*
 
 ### Breaking Changes