Add `export` section to usage

Adding `export` is allowed at the front of each line, this lets you
create a file that can be sourced by bash. This should be in the README.
Merge pull request #116 from oestrich/master

Add `export` section to usage
Watch .env for changes with Spring in Rails 4
use rbx-2 to fix travis issue
Merge pull request #118 from bkeepers/spring

Watch .env for changes with Spring in Rails 4
Merge pull request #119 from bkeepers/rbx-2

use rbx-2 to fix travis issue
.local.env
Merge remote-tracking branch 'origin/master' into nobody-expects-the-dotenv-concession

* origin/master:
  use rbx-2 to fix travis issue
  Watch .env for changes with Spring in Rails 4
  Add `export` section to usage

Conflicts:
	lib/dotenv-rails.rb