Re-add Sass Docs (#10364)

* Re-add Sass Docs

* Update built-in-css-support.md

* Apply lint-fix
Co-authored-by: NJJ Kasper <jj@jjsweb.site>

docs/basic-features/built-in-css-support.md

@@ -158,11 +158,23 @@ export default HelloWorld
 
 Please see the [styled-jsx documentation](https://github.com/zeit/styled-jsx) for more examples.
 
-## Sass, Less and Stylus Support
+## Sass Support
 
-To support importing `.scss`, `.sass`, `.less`, or `.styl` files you can use the following plugins:
+Next.js allows you to import Sass using both the `.scss` and `.sass` extensions.
+You can use component-level Sass via CSS Modules and the `.module.scss` or `.module.sass` extension.
+
+Before you can use Next.js' built-in Sass support, be sure to install [`sass`](https://github.com/sass/sass):
+
+```bash
+npm install sass
+```
+
+Sass support has the same benefits and restrictions as the built-in CSS support detailed above.
+
+## Less and Stylus Support
+
+To support importing `.less` or `.styl` files you can use the following plugins:
 
-- [@zeit/next-sass](https://github.com/zeit/next-plugins/tree/master/packages/next-sass)
 - [@zeit/next-less](https://github.com/zeit/next-plugins/tree/master/packages/next-less)
 - [@zeit/next-stylus](https://github.com/zeit/next-plugins/tree/master/packages/next-stylus)