Update CHANGELOG

Author: bouwew

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Ongoing
+
+- Change representation of no-thermostat-schedule-defined to a single `off` option via PR [#899](https://github.com/plugwise/python-plugwise/pull/899)
+
 ## v1.14.1
 
 - Improve manual fixtures script, reorder set_schedule_state() arguments for better compatibility with set_dhw_mode(), via PR[#897](https://github.com/plugwise/python-plugwise/pull/897)