📝 Update release notes

docs/en/docs/release-notes.md

@@ -2,6 +2,7 @@
 
 ## Latest Changes
 
+* 📝 Add docs recommending `Union` over `Optional` and migrate source examples. PR [#4908](https://github.com/tiangolo/fastapi/pull/4908) by [@tiangolo](https://github.com/tiangolo).
 * ✨ Add support for not needing `...` as default value in required Query(), Path(), Header(), etc.. PR [#4906](https://github.com/tiangolo/fastapi/pull/4906) by [@tiangolo](https://github.com/tiangolo).
 * 🎨 Fix default value as set in tutorial for Path Operations Advanced Configurations. PR [#4899](https://github.com/tiangolo/fastapi/pull/4899) by [@tiangolo](https://github.com/tiangolo).
 * ♻ Refactor dict value extraction to minimize key lookups `fastapi/utils.py`. PR [#3139](https://github.com/tiangolo/fastapi/pull/3139) by [@ShahriyarR](https://github.com/ShahriyarR).