add instructions to CHANGELOG

Author: ezhang6811

CHANGELOG.md

@@ -4,4 +4,10 @@ All notable changes to this project will be documented in this file.
 
 > **Note:** This CHANGELOG was created starting after version 2.11.4. Earlier changes are not documented here.
 
+For any change that affects end users of this package, please add an entry under the **Unreleased** section. Briefly summarize the change and provide the link to the PR. Example:
+- add SigV4 authentication for HTTP exporter
+  ([#1019](https://github.com/aws-observability/aws-otel-java-instrumentation/pull/1019))
+
+If your change does not need a CHANGELOG entry, add the "skip changelog" label to your PR.
+
 ## Unreleased