Merge pull request #428 from ElDeveloper/improve-docs

Improve docs on icon additions (thanks @ElDeveloper)

Author: bbrala

documentation/docs/customize.md

@@ -21,6 +21,8 @@ var items = {
 
 Font-Awesome icons used from [encharm/Font-Awesome-SVG-PNG](https://github.com/encharm/Font-Awesome-SVG-PNG). You can download more there if you like.
 
+Finally, you will need to re-build the CSS using [`sass`](http://sass-lang.com), otherwise you may see mismatchings between the icon references. In the `src` directory, run ``sass --update sass/``, two new CSS files will be created, these include the updated references to your new icons.
+
 ## Customize CSS
 
 You can use the _variables.scss to adjust variables on pretty much everything you want to change.