[docs] update README to avoid process.env.NODE_ENV (#7480)

closes #7417

Author: Rich-Harris

.changeset/little-seahorses-argue.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-static': patch
+---
+
+Update README

packages/adapter-static/README.md

@@ -162,7 +162,7 @@ You will have to prevent GitHub's provided Jekyll from managing your site by put
 A config for GitHub Pages might look like the following:
 
 ```js
-const dev = process.env.NODE_ENV === 'development';
+const dev = process.argv.includes('dev');
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {