make readme more up to date

README.md

@@ -32,13 +32,10 @@ below is an explanation of the folder structure:
     - `static/` - static files
       - `avatars/` - user avatar uploads
       - `badges/` - user badge uploads
-      - `css/` - CSS files generated from Sass sources
+      - `css/` - stylesheets
       - `emoji/` - emoji images used on the forum
       - `fonts/`
       - `js/`
-  - `sass/`
-    - `_default.scss` - the default theme. Sass variables that other themes modify are defined here, along with the default styles. other files define the available themes.
-  - `build-themes.sh` - script for building Sass files into CSS
   - `nginx.conf` - nginx config (production only)
   - `uwsgi.ini` - uwsgi config (production only)