docs: mention in README that the repo is archived (#389)

* docs: mention in README that the repo is archived

* shub feedback

* prb feedback

README.md

@@ -9,6 +9,14 @@
 [foundry]: https://getfoundry.sh/
 [foundry-badge]: https://img.shields.io/badge/Built%20with-Foundry-FFDB1C.svg
 
+## ⚠️ Archived
+
+This repository has been archived and is no longer maintained. For the latest contracts and updates, please visit the
+following repos:
+
+1. [Lockup Repo](https://github.com/sablier-labs/lockup/)
+2. [Airdrop Repo](https://github.com/sablier-labs/airdrops/)
+
 This repository contains the peripheral smart contracts of the Sablier V2 Protocol. For lower-level logic, see the
 [sablier-labs/v2-core](https://github.com/sablier-labs/v2-core) repository.