Revise README to reflect project status

Updated README to indicate that Microsite is no longer maintained and serves as a reference for islands architecture.

Author: natemoo-re

packages/microsite/README.md

@@ -1,3 +1,10 @@
+> [!CAUTION]
+> Microsite is no longer maintained. The partial hydration techniques pioneered in this project served as a precursor to [Astro](https://astro.build/), which [@natemoo-re](https://github.com/natemoo-re) co-created, and a number of other islands architecture-based frameworks like [Fresh](https://fresh.deno.dev/).
+> 
+> Consider this archive a reference implementation for islands architecture—may it inspire you to _do more with less JavaScript_.
+
+</div>
+
 <br />
 <br />
 
@@ -24,10 +31,6 @@ npm init microsite
 
 ---
 
-Microsite's public API is quite stable, but I caution **professional users** to consider this a WIP! There are plenty of quirks and bugs (especially with `dev` mode) that are being ironed out until Microsite reaches a more stable v2.0.0!
-
----
-
 Microsite is an **ESM node package**, so it needs to run in a Node environment which supports ESM. We support the latest version of [`node` v12.x LTS (Erbium)](https://nodejs.org/download/release/latest-v12.x/) — see [Engines](https://github.com/natemoo-re/microsite/blob/main/docs/engines.md) for more details.
 
 Ensure that your project includes `"type": "module"` in `package.json`, which will allow you to use ESM in your project's `node` scripts.