Dev command

[craigmulligan]

Currently, there isn't an easy way to run resin-electronjs on your local machine. You have to manually pass in a URL_LAUNCHER because it defaults to absolute path /usr/data/index.html.

We should also add an npm dev script for convenience (with doesn't start x server).

[danielmahon]

I use https://www.npmjs.com/package/dotenv and it seems to work nicely.