Update NEWS.md

Author: amartinhuertas

NEWS.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 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).
 
+## [0.6.6] - 2021.11.26
+
+### Added
+- Implemented `Base.setindex!`.
+
 ## [0.6.5] - 2021.10.20
 
 ### Fixed