Update docs changelog (for PR #60121) (#60626)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Sunbrye Ly <56200261+sunbrye@users.noreply.github.com>
Co-authored-by: sunbrye <sunbrye@github.com>

Author: 3 people

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Docs changelog
 
+**3 April 2026**
+
+We've published documentation for the GitHub Copilot SDK, now available in public preview. These docs were migrated from the `github/copilot-sdk` repo and cover getting started, setup, authentication, usage patterns, hooks, observability, integrations, and troubleshooting.
+
+See [GitHub Copilot SDK documentation](https://docs.github.com/en/copilot/how-tos/copilot-sdk).
+
+<hr>
+
 **2 April 2026**
 
 We've expanded the documentation for custom agents in Copilot CLI, adding information about the built-in agents.