Adding dotenv.

Hi Sahat,
First, great job on this project.  It's been an awesome reference and a great starter kit for a lot of my projects. Amazing :)

I wanted to add [dotenv](https://github.com/scottmotte/dotenv) -- it's small package that lets me have .env file in my directory -- untracked by git -- where I can store the values that I would be setting up in variables in heroku.  But this lets me "fake" them locally.  

Let me know what you think -- and if it's good to go, I'll add in some docs to readme.  

Thanks!