[Docs] Update changelog

Author: lindyhopchris

CHANGELOG.md

@@ -3,6 +3,17 @@
 All notable changes to this project will be documented in this file. This project adheres to
 [Semantic Versioning](http://semver.org/) and [this changelog format](http://keepachangelog.com/).
 
+## Unreleased (2.0)
+
+### Added
+
+- Package now supports PHP 8.1.
+- Upgraded to v2 of the `laravel-json-api/eloquent` dependency.
+
+### Changed
+
+- Added return types to internal methods to remove deprecation messages in PHP 8.1.
+
 ## [1.0.0] - 2021-07-21
 
 Initial release. This brought in the code from `laravel-json-api/eloquent:1.0.0-beta.6`, with the only changes being new