Update Changelog

Author: bouwew

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Update `_last_used_schedule()`: provide the collected schedules as input in order to find the last-modified valid schedule.
 - `_rule_ids_by_x()`: replace None by NONE, allowing for simpler typing.
 - Remove `schedule_temperature` from output: for Adam the schedule temperature cannot be collected when a schedule is not active.
+- Improve solution for plugwise-beta issue #276
 
 # v0.18.3: Smile: move solution for https://github.com/plugwise/plugwise-beta/issues/276 into backend