docs(changelog): reference MIGRATION.md

closes #1539

Author: RobertCraigie

CHANGELOG.md

@@ -53,6 +53,8 @@ Full Changelog: [v5.0.0...v5.0.1](https://github.com/openai/openai-node/compare/
 
 ## 5.0.0 (2025-05-29)
 
+This release migrates from node-fetch to builtin fetch, for full release notes see [MIGRATION.md](https://github.com/openai/openai-node/blob/master/MIGRATION.md).
+
 Full Changelog: [v5.0.0-alpha.0...v5.0.0](https://github.com/openai/openai-node/compare/v5.0.0-alpha.0...v5.0.0)
 
 ### Features