Updated Readme to include environment variables info

README.md

@@ -67,6 +67,20 @@ You can use ES6 and use both relative imports or import libraries from npm.
 Any CSS file directly under the `src/css/` folder will get compiled with [PostCSS Next](http://cssnext.io/)
 to `/dist/css/{filename}.css`. Import statements will be resolved as part of the build
 
+## Environment variables
+
+Two seperate the development and production *- aka build -* stages, all gulp
+tasks run with a node environment variable named either `development` or 
+`production`.
+
+You can access the environment variable inside the theme files with 
+`getenv "NODE_ENV"`. See the following example for a conditional statement:
+
+    {{ if eq (getenv "NODE_ENV") "development" }}You're in development!{{ end }}
+
+All tasks starting with *build* set the environment variable to `production` - 
+the other will set it to `development`.
+
 ## Deploying to netlify
 
 - Push your clone to your own GitHub repository.