Update README.md: add custom CSS in config options

README.md

@@ -26,6 +26,7 @@
   - [Front Matter example](#front-matter-example)
   - [Configuration options](#configuration-options)
     - [Columns](#columns)
+    - [Custom CSS](#custom-css)
     - [Post Meta](#post-meta)
     - [Related Content](#related-content)
     - [Share Buttons](#share-buttons)
@@ -97,7 +98,7 @@ hugo server
 
 Now you can go to [localhost:1313](http://localhost:1313) webpage and the Binario theme should be visible.
 
-After you make sure that **Binario** works, you may start customizing the theme. You can change [number of columns](#columns), activate [footer social icons](#footer-social-icons), [share buttons](#share-buttons) and much more.
+After you make sure that **Binario** works, you may start customizing the theme if it's needed. You can change [number of columns](#columns), activate [footer social icons](#footer-social-icons), [share buttons](#share-buttons) and [much more](#configuration-options).
 
 ## Configuration
 
@@ -229,6 +230,24 @@ Binario includes some customizable configuration options that may be useful.
 
 By default, Binario works with two columns layout (if it possible by screen size) for list pages, but you can also use one column or three columns layout. Change `Params.columns`to preferable value (from 1 to 3). You can also change this option for specific list pages.
 
+#### Custom CSS
+
+If you want to include custom CSS files, you need to assign an array of references in site config file (`config.toml` by default) like following:
+
+```toml
+[Params]
+  customCSS = ["css/custom.css"]
+```
+
+Of course, you can reference as many CSS files as you want. Their paths need to be relative to the `static` folder of your Hugo site:
+
+```toml
+[Params]
+  customCSS = ["css/custom.css", "css/another.css"]
+```
+
+All these CSS files will be added through the `head.html` partial after the built-in CSS file.
+
 #### Post Meta
 
 You may activate post meta fields with `.Site.Params.post_meta` parameter.