Update CHANGELOG

Author: loafoe

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## v0.8.4
+- Add additional error messages
+
+## v0.8.3
+- Fix documentation
+
 ## v0.8.2
 - Refactor CDR resource naming after some trial use
 - Add `part_of` attribute to `hsdp_cdr_org`