mention vite, explain config options

Author: Rich Harris

content/tutorial/03-sveltekit/01-concepts/01-introducing-sveltekit/README.md

@@ -30,6 +30,8 @@ On the right, in the file tree viewer, you'll see a handful of files that Svelte
 
 `svelte.config.js` contains your project configuration. We don't need to worry about this file for now, but if you're curious, [visit the documentation](https://kit.svelte.dev/docs/configuration).
 
+`vite.config.js` contains the [Vite](https://vitejs.dev/) configuration. Because SvelteKit uses Vite, you can use [Vite features](https://vitejs.dev/guide/features.html) like hot module replacement, TypeScript support, static asset handling and so on.
+
 `src` is where your app's source code goes. `src/app.html` is your page template (SvelteKit replaces the `%sveltekit.head%` and `%sveltekit.body%` as appropriate), and `src/routes` defines the [routes](/tutorial/pages) of your app.
 
 Finally, `static` contains any assets (like a `favicon.png` or a `robots.txt`) that should be included when your app is deployed.

content/tutorial/common/svelte.config.js

@@ -9,6 +9,8 @@ const config = {
 
 	vitePlugin: {
 		experimental: {
+			// This feature enables compile-time warnings to be
+			// visible in the learn.svelte.dev editor
 			sendWarningsToBrowser: true
 		}
 	}

content/tutorial/common/vite.config.js

@@ -3,6 +3,9 @@ import { defineConfig } from 'vite';
 
 export default defineConfig({
 	plugins: [sveltekit()],
+
+	// Normally this would be unnecessary, but we
+	// need it for learn.svelte.dev
 	server: {
 		fs: {
 			strict: false