Update README.md

Author: simonexmachina

README.md

@@ -16,6 +16,10 @@ ember-cli-sass uses libsass to preprocess your ember-cli app's files and provide
 ember install ember-cli-sass
 ```
 
+### Addon Development
+
+If you want to using ember-cli-sass in an addon and you want to distribute the compiled CSS it must be installed as a `dependency` so that `addon/styles/addon.scss` is compiled into `dist/assets/vendor.css`. This can be done using `npm install --save ember-cli-sass`.
+
 ## Usage
 
 By default this addon will compile `app/styles/app.scss` into `dist/assets/app.css` and produce