Clarify repository move and archival status

Updated README to indicate repository move and archival status.

Author: infiniteregrets

README.md

@@ -24,6 +24,11 @@
   </p>
 </div>
 
+> [!NOTE]
+> **Repository moved:** The S2 CLI is now maintained in the
+> [`s2-streamstore/s2`](https://github.com/s2-streamstore/s2) repository.
+> This repository is archived and kept for historical reference only.
+
 Command Line Interface to interact with the
 [S2 API](https://s2.dev/docs/rest/protocol).