More detailed steps for basic usage

It could be just me, but when using this in another project after a while I was perplexed why things weren't working after looking at the README.

Then it hit me when looking back over some old apps that I still needed to use `.load` when using what appears to be a normal convention of placing a `.env` in the same directory your build tool (Gulp/Grunt/etc) is.

Let me know if I'm way off or something else might be better!