soften language for d/l time saved, + GZip note

https://github.com/substack/browserify-handbook#window-globals
>This approach tends to be very slow since each <script> tag initiates a new round-trip http request...
> loads much faster because only a single http request for a single <script> tag needs to execute

Honestly, I think improved speed depends on the resources needed for the app & loading order.  A few external resources hosted on a CDN or separate server (with unique originating URL) could load concurrently, thanks to most browsers having spare [Max Connections](http://www.browserscope.org/?category=network&v=top).  A browserified/concocted chunk may have to wait for open HTTP connection, since "Connections per Hostname" has a smaller cap.  True, an extra HTTP lookup is needed, but lookup time [can be reduced](https://developer.mozilla.org/en-US/docs/Controlling_DNS_prefetching), & IP &/or file may be cached already.|
I did note the extra GZip reduction.  But even at best 10 browserified files may save 10 HTTP *packets*, likely 5, so a few Kilobytes?
Since there are so many variables, I softened the language of the impact.

I'm willing to see some hard proofs either way.