Update readme on SCSS opt-in

Author: johanbrook

Diff for: README.md

@@ -8,6 +8,7 @@ Usually, building HTML emails yourself is tedious. On top of that, add the need
 
 - **Server side rendering** with the [Meteor SSR](https://github.com/meteorhacks/meteor-ssr/) package. Use Blaze features and helpers like on the client.
 - **CSS inlining** with [Juice](http://npmjs.org/package/juice). No extra build step.
+- **SCSS support** using `node-sass` (opt-in).
 - **Preview and debug** emails in development mode in your browser when developing.
 - **Layouts** for re-using markup.
 
@@ -25,6 +26,14 @@ meteor add lookback:emails
 
 A `Mailer` global will exported on the *server*.
 
+**Notice.** If you want SCSS support, be sure to add the `[meteor-node-sass](https://github.com/chrisbutler/meteor-node-sass)` package to your app:
+
+```
+meteor add chrisbutler:node-sass
+```
+
+`lookback:emails` will automatically detect `node-sass` being available, and will be able to compile `.scss` files.
+
 ## Sample app
 
 There is a sample application in this repo, in the `example` directory. Boot it up, and preview an email with: