CHANGELOG: mention new umoci-stat features

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Author: cyphar

CHANGELOG.md

@@ -14,6 +14,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased] ##
 
+### Added ###
+* `umoci stat` now includes information about the manifest and configuration of
+  the image, both in the regular and JSON-formatted outputs.
+
 ### Fixed ###
 * Some minor aspects of how `umoci stat` would filter special characters in
   history entries have been resolved.