docs: precise plugin-react-swc build when using plugins (#12020)

Author: ArnaudBarre

docs/plugins/index.md

@@ -22,11 +22,11 @@ Check out [Using Plugins](../guide/using-plugins) for information on how to use
 
 ### [@vitejs/plugin-react](https://github.com/vitejs/vite-plugin-react/tree/main/packages/plugin-react)
 
-- Uses esbuild and Babel, achieving fast HMR with a small package footprint and the flexibility of being able to use the Babel transform pipeline.
+- Uses esbuild and Babel, achieving fast HMR with a small package footprint and the flexibility of being able to use the Babel transform pipeline. Without additional Babel plugins, only esbuild is used during builds.
 
 ### [@vitejs/plugin-react-swc](https://github.com/vitejs/vite-plugin-react-swc)
 
-- Uses esbuild during build, but replaces Babel with SWC during development. For big projects that don't require non-standard React extensions, cold start and Hot Module Replacement (HMR) can be significantly faster.
+- Replaces Babel with SWC during development. During builds, SWC+esbuild are used when using plugins, and esbuild only otherwise. For big projects that don't require non-standard React extensions, cold start and Hot Module Replacement (HMR) can be significantly faster.
 
 ### [@vitejs/plugin-legacy](https://github.com/vitejs/vite/tree/main/packages/plugin-legacy)