Update react hot loader documentation

[dillonbailey]

Based on the most recent react hot loader documentation https://github.com/gaearon/react-hot-loader and references, I do not think the current webpack/browsersync setup is utilising the "next" version of 4.0.0 correctly.

[dillonbailey]

@greypants I'll try to get around to setting up a PR for this issue once I get a working solution. It may be more "Out of the box" than I originally thought - was having some weird build errors yesterday due to naming conventions, but I do think it's a worthwhile topic to bring up to speed as the documentation says "next" for RHL.

Cheers!