update CHANGELOG.md do-not-edit comment to match attrs style

Assisted-by: Claude Opus 4.6

Author: MikeGoldsmith

CHANGELOG.md

@@ -2,8 +2,13 @@
 
 All notable changes to this project will be documented in this file.
 
-<!-- DO NOT EDIT THIS FILE DIRECTLY. Instead, add a changelog fragment
-     in the .changelog/ directory. See CONTRIBUTING.md for details. -->
+<!--
+Do *NOT* add changelog entries here!
+
+This changelog is managed by towncrier and is compiled at release time.
+
+See https://github.com/open-telemetry/opentelemetry-python/blob/main/CONTRIBUTING.md#changelog for details.
+-->
 
 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).