Add RFC5 to version history (#28)

Author: jo-mueller

ngff_spec/version_history.md

@@ -8,6 +8,12 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [0.6dev1] - 2025-11-18
+
+### Added
+
+Initial proposal for RFC-5: Transforms. [See proposal text](https://ngff.openmicroscopy.org/rfc/5/versions/1/index.html).
+
 ## [0.5.2] - 2025-01-10
 
 ### Changed