Add CHANGELOG entry for platform discovery mechanism

Add an entry to the CHANGELOG for v0.0.58 to document the new platform discovery
mechanism added in commit [1]

[1] ff9fac6

Change-Id: I6259588bba8be86d686dd633aa4a14aa34f4567d

Author: calancha

doc/reference/CHANGELOG.md

@@ -28,6 +28,9 @@ All notable changes to this project will be documented in this file.
 - weeder: update ubi9-python-39 container
 - The Zuul label to run gate pipelines changed from `gateit` to `workflow`.
 - Container images based on UBI have been updated. Zuul and Nodepool services will be restarted during the upgrade.
+- A new platform discovery mechanism has been added to the Software Factory CLI, allowing it
+  to automatically detect the Kubernetes distribution in use. As a consequence, the `OPENSHIFT_USER`
+  environment variable is now optional.
 
 ### Removed