Mention Rollup (#2187)

content/docs/code-splitting.md

@@ -7,7 +7,8 @@ permalink: docs/code-splitting.html
 ## Bundling {#bundling}
 
 Most React apps will have their files "bundled" using tools like
-[Webpack](https://webpack.js.org/) or [Browserify](http://browserify.org/).
+[Webpack](https://webpack.js.org/), [Rollup](https://rollupjs.org/) or 
+[Browserify](http://browserify.org/).
 Bundling is the process of following imported files and merging them into a
 single file: a "bundle". This bundle can then be included on a webpage to load
 an entire app at once.