chore: update README for repository archival (#1142)

Co-authored-by: Mackenzie Zastrow <zastrowm@users.noreply.github.com>

Author: zastrowm

README.md

@@ -1,3 +1,15 @@
+<div align="center">
+
+### :warning: This repository has been archived
+
+**The TypeScript SDK has moved to the [strands-agents/harness-sdk](https://github.com/strands-agents/harness-sdk) monorepo.**
+
+The source code is now under [`strands-ts/`](https://github.com/strands-agents/harness-sdk/tree/main/strands-ts). All new development, issues, and pull requests should go there.
+
+</div>
+
+---
+
 <div align="center">
   <div>
     <a href="https://strandsagents.com">