Add a readme section with a little more information about using HMR.
Add a readme section with a little more information about using HMR.

Fixes #5 somewhat.

AgentME/browserify-hmr,AgentME/browserify-hmr,AgentME/browserify-hmr,royriojas/browserify-hmr,royriojas/browserify-hmr,royriojas/browserify-hmr