docs: add changelog entry

Author: DannyvdSluijs

CHANGELOG.md

@@ -6,6 +6,9 @@ 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]
+### Added
+- Welcome first time contributors ([#782](https://github.com/jsonrainbow/json-schema/pull/782))
+
 ### Changed
 - Used PHPStan's int-mask-of<T> type where applicable ([#779](https://github.com/jsonrainbow/json-schema/pull/779))
 - Fixed some PHPStan errors ([#781](https://github.com/jsonrainbow/json-schema/pull/781))