Update 00-what-is-rollup.md

important comma - "fewer bigger files" without the comma meant that rather than "fewer files, but larger in size", the guide talked about "fewer files that are big", which is pretty much the opposite of the point this sentence tries to make.

src/guide/00-what-is-rollup.md

@@ -53,6 +53,6 @@ For one thing, ES2015 modules don't yet work in browsers or Node.js, so we need
 But there are also some major advantages to bundling your code:
 
 * A bundle is more portable and easier to consume than a collection of files
-* Compression works better with fewer bigger files than with lots of small ones
+* Compression works better with fewer, bigger files than with lots of small ones
 * In the browser, a 100kb bundle loads much faster than 5 20kb files (that will change when HTTP/2 gains widespread adoption, but we're not there yet)
 * By bundling code, we can take advantage of [tree-shaking](#what-is-tree-shaking-), resulting in fewer wasted bytes