docs: add release "release/teak-rg.1" tag to the CHANGELOG

tag is used in teak-rg release

Author: ihor-romaniuk

RG_CHANGELOG.rst

@@ -0,0 +1,18 @@
+RG Changelog
+############
+
+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 customized Semantic Versioning e.g.: `teak-rg.1`
+
+[Unreleased]
+************
+
+[release/teak-rg.1] - 2025-08-06
+********************************
+
+Added:
+======
+* add direct import of openedx-brand overrides (TEA-18)
+* add design tokens support (TEA-18)