docs: Add link to external changelog.

Author: rogerluan

CHANGELOG.md

@@ -1,10 +1,13 @@
-# context_sdk Changelog
+# Changelog
 
-**[Flutter] 1.1.0 - 2024-10-16**
+All notable changes to this project are documented externally.
 
-- Update to ContextSDK 4.7.0 on iOS
+For a complete changelog, please visit: https://docs.decision.contextsdk.com/changelog/
+
+## [Flutter] 1.1.0 - 2024-10-16
 
+- Update to ContextSDK 4.7.0 on iOS
 
-**[Flutter] 1.0.0 - 2024-10-01**
+## [Flutter] 1.0.0 - 2024-10-01
 
 - Initial Release