Update history.adoc for #584

This was not included in PR #586 because the working draft of 1.13 hadn't been created

Author: JonathanGregory

history.adoc

@@ -7,6 +7,8 @@
 
 === Version 1.13-draft
 
+* {issues}584[Issue #584]:  Allow `Z` as time-zone offset, with a couple of examples, and allow time-zone offset with date alone, both being consistent with UDUNITS syntax.
+
 === Version 1.12 (04 December 2024)
 
 * {issues}513[Issue #513]: Include DOI and License information in the conventions document