Docs: Update Stylesheets README (#37034)

Looks like we missed this when updating styling docs (#35779).

Author: ockham

client/assets/stylesheets/README.md

@@ -1,12 +1,7 @@
-Styles
-======
+# Styles
 
-Calypso uses Sass to build its CSS and compile it to `public/style.css`. Remember that all styles end up in a single file, so all styles will apply to every page, all the time. Make sure you namespace your styles for the page you are working on.
+Calypso uses Sass to build its CSS. Remember that all styles, even when loaded at different times, eventually end up on one page as part of a single HTML document. Make sure you namespace your styles for the page you are working on.
 
-### Adding a new Sass file
-
-If you are adding a new Sass file to `assets/stylesheets` you will need to reference the file in `assets/stylesheets/style.scss` for it to load. We have three directories to organize the respective files: layout, sections, and shared. If you are adding a new file you are likely adding it to `sections`.
-
-Component specific stylesheets are referenced in the file `assets/stylesheets/_components.scss`.
+This directory contains styling that is applied globally, such as resets and animations. You shouldn't typically need to add a new Sass file to this directory if you just want to style a newly added component.
 
 Check [our styleguide](https://github.com/Automattic/wp-calypso/blob/master/docs/coding-guidelines/css.md) for more information on how we use Sass.