Docs: note that the first-contract tutorial targets Linux

Windows and macOS walkthroughs will follow later.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hsyl20

tutorials/first-smart-contract.md

@@ -1,12 +1,15 @@
 ---
-title: Your first smart contract with Plinth
+title: Your first smart contract with Plinth (Linux)
 permalink: /tutorials/first-smart-contract/
 ---
 Before writing a real validator, it helps to get the whole toolchain working
 end to end with the simplest possible Plinth program: a function that adds two
 numbers. In this tutorial you will create a tiny project from scratch, compile
 it with `uplc-ghc`, run it, and read the Plutus Core it produced.
 
+This tutorial targets **Linux**. Windows and macOS walkthroughs will follow
+later.
+
 ## Before you start
 
 You need a built `uplc-ghc`. If you have not built it yet, follow

tutorials/index.md

@@ -6,4 +6,5 @@ permalink: /tutorials/
 guaranteed-to-work experience so you can learn by doing. They are for newcomers
 who want to get started, not for looking up specific facts.
 
-- [Your first smart contract with Plinth]({% link tutorials/first-smart-contract.md %})
+- [Your first smart contract with Plinth (Linux)]({% link tutorials/first-smart-contract.md %})
+  — targets Linux; Windows and macOS walkthroughs will follow later.