Added missing configuration reference items to docs

Author: gorkalaucirica

docs/first_use_installing_and_configuring.md

@@ -21,6 +21,8 @@ lin3s_pattern_library_builder:
         custom_styles:
             color_primary: "#000"
         logo: ~
+        javascripts: []
+        stylesheets: []
     templates_config_files_path: "%kernel.root_dir%/PatternLibrary"
 ```
 Add routes to access the Design System in your routing file:

docs/symfony_configuration_reference.md

@@ -10,5 +10,9 @@ lin3s_pattern_library_builder:
         custom_styles:
             color_primary: "#000"
         logo: ~
+        # Javascript files to be injected to the pattern library
+        javascripts: []
+        # CSS files to be injected to the pattern library
+        stylesheets: []
     templates_config_files_path: "%kernel.root_dir%/PatternLibrary"
 ```