Update readme

Add instructions about modifying theme color or fonts, see #66

README.md

@@ -95,14 +95,16 @@ We only have built-in support for Disqus at the moment, if that doesn't fit your
 ##### Add custom analytics
 If you prefer to use different analytics system other than google analytics, then add them inside `layouts/partials/analytics.html`.
 
-#### Add custom css
+#### Customize CSS
 
-For adding custom css to the theme, you need to assign an array of references in `config.toml` like following:
+If you'd like to customize theme color or fonts, you can simply override `assets/scss/_predefined.scss`, by simply copy it to site's root (keep the same relative path) then edit those variables. But keep in mind, you'll need **Hugo extended version** which has the ability to rebuild SCSS. You don't have to use extended version in production but in this case it's necessary to make sure the `resources` folder is committed and "up to date" (by running `hugo` or `hugo server` locally using the extended version). But anyway, always use the extended version if you can.
+
+For adding other custom CSS to the theme, you can assign an array of references in `config.toml` like following:
 ```
 [params]
   customCSS = ["css/foo.css", "css/bar.css"]
 ```
-You can reference as many stylesheets as you want. Their paths need to be relative to the `static` folder or they can be network resources.
+You may reference as many stylesheets as you want. Their paths need to be relative to the `static` folder or it can be a full URL for external resources.
 
 #### Code injection