Fix stylelint violations

In #1148 we introduce `stylelint`. However, the empty styles introduced
in #1145 are empty file violations. By adding comments, we avoid that
error.

Note that we need to add these comments because there's no way to
automatically fix those violations with something like `prettier`.

lib/generators/suspenders/styles_generator.rb

@@ -25,8 +25,13 @@ def build_directory_structure
         return if is_tailwind?
 
         create_file "app/assets/stylesheets/base.css"
+        append_to_file "app/assets/stylesheets/base.css", "/* Base Styles */"
+
         create_file "app/assets/stylesheets/components.css"
+        append_to_file "app/assets/stylesheets/components.css", "/* Component Styles */"
+
         create_file "app/assets/stylesheets/utilities.css"
+        append_to_file "app/assets/stylesheets/utilities.css", "/* Utility Styles */"
       end
 
       # Modify if https://github.com/rails/cssbundling-rails/pull/139 is merged

test/generators/suspenders/styles_generator_test.rb

@@ -186,9 +186,15 @@ class StylesGenerator::PostCssTest < Rails::Generators::TestCase
       test "creates stylesheets" do
         run_generator
 
-        assert_file app_root("app/assets/stylesheets/base.css")
-        assert_file app_root("app/assets/stylesheets/components.css")
-        assert_file app_root("app/assets/stylesheets/utilities.css")
+        assert_file app_root("app/assets/stylesheets/base.css") do |file|
+          assert_equal "/* Base Styles */", file
+        end
+        assert_file app_root("app/assets/stylesheets/components.css") do |file|
+          assert_equal "/* Component Styles */", file
+        end
+        assert_file app_root("app/assets/stylesheets/utilities.css") do |file|
+          assert_equal "/* Utility Styles */", file
+        end
       end
 
       private