Update Nix setup instructions in README

Reorganize Nix setup instructions for clarity.

README.md

@@ -83,15 +83,18 @@ npm run start
 ## Nix Setup
 
 If using Nix:
-```bash
-./run.sh
-```
 
-The script will:
-- Run `npm run pre-build` to install dependencies and Chromium  
-- Then start the script headlessly using `xvfb-run`
+1. Run the pre-build step first:
+   ```bash
+   npm run pre-build
+   ```
 
----
+2. Then start the script:
+   ```bash
+   ./run.sh
+   ```
+
+This will launch the script headlessly using `xvfb-run`.
 
 ## Docker Setup