doc: add clarification about axis name to version history

Author: jo-mueller

version_history.md

@@ -23,6 +23,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - specification: Changed the constraints for valid `path` values in `wells` for HCS plates to allow some non-alphanumeric characters.
 - specification: Corrected that `version` field is not required under plate/well/labels metadata. 
 - specification: Constrained datatype of multiscales datasets to be the same across all resolutions
+- specification: Clarified that `name` field in `axes` metadata is required to be a non-empty string.
 - style: Adopted JSON terminology for "object" and "array" in the spec document.
 
 ### Removed