docs: mention breaking change from vitejs#8049

docs/guide/migration.md

@@ -52,6 +52,10 @@ If using ESM for SSR isn't possible in your project, you can set `ssr.format: 'c
 ## General Changes
 
 - JS file extensions in SSR and lib mode now use a valid extension (`js`, `mjs`, or `cjs`) for output JS entries and chunks based on their format and the package type.
+- Terser is now an optional dependency. If you are using `build.minify: 'terser'`, you need to install it.
+  ```shell
+  npm add -D terser
+  ```
 
 ### `import.meta.glob`