Add changelog

Author: W0rma

CHANGELOG.md

@@ -30,6 +30,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `strict_types=1` to all classes in ./src ([#758](https://github.com/jsonrainbow/json-schema/pull/758))
 - Raise minimum level of marc-mabe/php-enum ([#766](https://github.com/jsonrainbow/json-schema/pull/766))
 - Cleanup test from @param annotations ([#768](https://github.com/jsonrainbow/json-schema/pull/768))
+- Remove obsolete PHP 7.1 version check ([#772](https://github.com/jsonrainbow/json-schema/pull/772))
 
 ## [6.0.0] - 2024-07-30
 ### Added