Add 0.8.1 release notes

Author: shyiko

CHANGELOG.md

@@ -5,7 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased](https://github.com/altinity/ice/compare/v0.8.0...master)
+## [Unreleased](https://github.com/altinity/ice/compare/v0.8.1...master)
+
+## [0.8.1](https://github.com/altinity/ice/compare/v0.8.0...v0.8.1)
+
+### Fixed
+- ice: nullCount metric calculation.
 
 ## [0.8.0](https://github.com/altinity/ice/compare/v0.7.3...v0.8.0)