[Docs] Update changelog and tag initial version

Author: lindyhopchris

CHANGELOG.md

@@ -3,4 +3,7 @@
 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
+## [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
+namespaces.