[Encore] Proactively warn the user that enableSassLoader() needs additional packages

Author: Lyrkan

frontend/encore/simple-example.rst

@@ -65,6 +65,9 @@ Inside, use Encore to help generate your Webpack configuration.
 This is already a rich setup: it outputs 2 files, uses the Sass pre-processor and
 enables source maps to help debugging.
 
+Actually, to use ``enableSassLoader()``, you'll need to install a few
+more packages. But Encore will tell you *exactly* what you need after running it.
+
 .. _encore-build-assets:
 
 To build the assets, use the ``encore`` executable:
@@ -89,9 +92,6 @@ To build the assets, use the ``encore`` executable:
 
     Re-run ``encore`` each time you update your ``webpack.config.js`` file.
 
-Actually, to use ``enableSassLoader()``, you'll need to install a few
-more packages. But Encore will tell you *exactly* what you need.
-
 After running one of these commands, you can now add ``script`` and ``link`` tags
 to the new, compiled assets (e.g. ``/build/app.css`` and ``/build/app.js``).
 In Symfony, use the ``asset()`` helper: