Add comment to one line of example

[tristanleboss]

trafficstars

Hello,

I was reading the Usage section of the README.md file and one line lack a comment :

if (!module.hot.data) {

I have no ideea what this line does. I checked the WebPack HMR API doc and found one occurence of this property (https://webpack-v3.jsx.app/api/hot-module-replacement/):

This object will be available at module.hot.data after the update.

But it doesn't explain what's its purpose and what checking its existence implies.

Adding a comment to this line may help futur reader.