CHANGELOG: add 0.8.0 release notes

CHANGELOG.md

@@ -3,9 +3,18 @@
 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]: https://github.com/gg-scm/gg-git/compare/v0.7.3...main
+[Unreleased]: https://github.com/gg-scm/gg-git/compare/v0.8.0...main
 
-## [Unreleased][]
+## [0.8.0][] - 2020-12-31
+
+Version 0.8 adds two new packages: `object` and `packfile`. These are pure Go
+implementations of the Git data structures and wire protocol, respectively.
+While most users will not interact with these packages directly, this provides
+better correctness guarantees, and makes it easier to directly read or write
+objects to a Git repository. Users that inspect commits with the `git` package
+now receive a higher fidelity data structure than before.
+
+[0.8.0]: https://github.com/gg-scm/gg-git/releases/tag/v0.8.0
 
 ### Added