Fix Next docs configuration structure for PostCSS plugins

Author: MoOx

packages/website/docs/learn/environment-setup/02-next.md

@@ -54,18 +54,19 @@ export default config;
 import babelLoader from "./babelLoader.config.js";
 
 const config = {
-  plugins: [
+  plugins: {
     "react-strict-dom/postcss-plugin": {
       include: [
         // Include source files to watch for style changes
+        // Be specific and avoid a non specific glob like "**/*.{js,jsx}" which could cause major performance issues during build
         'src/**/*.{js,jsx,mjs,ts,tsx}',
         // List any installed node_modules that include UI built with React Strict DOM
         'node_modules/<package-name>/*.js'
       ],
       babelConfig: babelLoader,
       useLayers: true,
     }
-  ],
+  },
 };
 
 export default config;