docs: add banner info

Author: bluwy

docs/config/build-options.md

@@ -229,6 +229,27 @@ If the `fileName` ends with `.json`, the raw JSON metadata will be generated ins
 ]
 ```
 
+::: tip
+If you'd like to reference the license file in the built code, you can use `build.rollupOptions.output.banner` to inject a comment at the top of the files. For example:
+
+```js twoslash [vite.config.js]
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    license: true,
+    rollupOptions: {
+      output: {
+        banner:
+          '/* See licenses of bundled dependencies at https://example.com/license.md */',
+      },
+    },
+  },
+})
+```
+
+:::
+
 ## build.manifest
 
 - **Type:** `boolean | string`