Add a section for changelog entries that pertain to the next patch release.

This will make it easier to keep changelogs synced between develop and stable branches.

CHANGELOG.md

@@ -21,6 +21,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Fixed
 - Support pagination in conversations API
 
+## [unreleased-patch]
+
 ## [2.0.2] - 2020-04-08
 ### Added
 - Support for Funkwhale's `Audio` activity