Add note about having to run astro build before astro preview

src/content/docs/en/reference/cli-reference.mdx

@@ -224,9 +224,9 @@ Can be combined with the [common flags](#common-flags) documented below.
 
 ## `astro preview`
 
-Starts a local server to serve your static `dist/` directory.
+Starts a local server to serve the contents of your static directory (`dist/` by default) created by running `astro build`.
 
-This command is useful for previewing your build locally, before deploying it. It is not designed to be run in production. For help with production hosting, check out our guide on [Deploying an Astro Website](/en/guides/deploy/).
+This command allows you to preview your site locally [after building](#astro-build) to catch any errors in your build output before deploying it. It is not designed to be run in production. For help with production hosting, check out our guide on [Deploying an Astro Website](/en/guides/deploy/).
 
 Since Astro 1.5.0, `astro preview` also works for SSR builds if you use an adapter that supports it. Currently, only the [Node adapter](/en/guides/integrations-guide/node/) supports `astro preview`.