update adapter-static readme

packages/adapter-static/README.md

@@ -16,7 +16,8 @@ export default {
 			// default options are shown
 			pages: 'build',
 			assets: 'build',
-			fallback: null
+			fallback: null,
+			precompress: false
 		})
 	}
 };
@@ -38,6 +39,10 @@ The directory to write static assets (the contents of `static`, plus client-side
 
 Specify a fallback page for SPA mode, e.g. `index.html` or `200.html` or `404.html`.
 
+### precompress
+
+If `true`, precompresses files with brotli and gzip. This will generate `.br` and `.gz` files.
+
 ## SPA mode
 
 You can use `adapter-static` to create a single-page app or SPA by specifying a **fallback page**.