add changelog entry

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
 ## [Unreleased patch]
+### Changed
+- Polls will be hidden with status content if "Collapse posts with subjects" is enabled and the post is collapsed.
 
 ## [2.1.0] - 2020-08-28
 ### Added