docs: Better indicate include options in sass setup.

Author: Kelketek

site/content/docs/5.3/customize/sass.md

@@ -73,14 +73,15 @@ In your `custom.scss`, you'll import Bootstrap's source Sass files. You have two
 @import "../node_modules/bootstrap/scss/mixins";
 @import "../node_modules/bootstrap/scss/root";
 
-// 6. Optionally include any other parts as needed
+// 6. Include any other optional stylesheet partials as desired; list below is not inclusive of all available stylesheets
 @import "../node_modules/bootstrap/scss/utilities";
 @import "../node_modules/bootstrap/scss/reboot";
 @import "../node_modules/bootstrap/scss/type";
 @import "../node_modules/bootstrap/scss/images";
 @import "../node_modules/bootstrap/scss/containers";
 @import "../node_modules/bootstrap/scss/grid";
 @import "../node_modules/bootstrap/scss/helpers";
+// ...
 
 // 7. Optionally include utilities API last to generate classes based on the Sass map in `_utilities.scss`
 @import "../node_modules/bootstrap/scss/utilities/api";