docs: add section to build guide

docs/guide/build.md

@@ -43,6 +43,20 @@ module.exports = defineConfig({
 
 For example, you can specify multiple Rollup outputs with plugins that are only applied during build.
 
+## Chunking Strategy
+
+You can configure how chunks are split using `build.rollupOptions.manualChunks` (see [Rollup docs](https://rollupjs.org/guide/en/#outputmanualchunks)). Until Vite 2.7, the default chunking strategy divided the chunks into `index` and `vendor`. It is a good strategy for some SPAs, but it is hard to provide a general solution for every Vite target use case. From Vite 2.8, `manualChunks` is no longer modified by default. You can continue to use the Split Vendor Chunk strategy by adding the `splitVendorChunkPlugin` in your config file:
+
+```js
+// vite.config.js
+import { splitVendorChunkPlugin } from 'vite'
+module.exports = defineConfig({
+  plugins: [splitVendorChunkPlugin()]
+})
+```
+
+This strategy is also provided as a `splitVendorChunk({ cache: SplitVendorChunkCache )` factory, in case composition with custom logic is needed. `cache.reset()` needs to be called at `buildStart` for build watch mode to work correctly in this case.
+
 ## Rebuild on files changes
 
 You can enable rollup watcher with `vite build --watch`. Or, you can directly adjust the underlying [`WatcherOptions`](https://rollupjs.org/guide/en/#watch-options) via `build.watch`: