CHANGELOG: add missing release, boilerplate [Unreleased] section

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+## [2.0.0] - 2022-05-01
+
 ## [1.3.0] - 2021-07-02
 ### Changed
 - Layout: show right sidebar on all pages.