Add changelog for 0.8.2

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

CHANGELOG.md

 # Changelog
 All notable changes to this project will be documented in this file.
 
+## 0.8.2 – 2018-06-28
+### Added
+- Advanced search
+- New and updated translations
+### Fixed
+- Preserve URI hash in sanitized HTML messages
+- Pagination of incoming messages
+- Autoconfig issues
+- Security issues in third party JavaScript libraries
+- Folder sorting
+- Issue template URL in README
+
 ## 0.8.1 – 2018-05-14
 ### Added
 - New and updated translations