Document txt icon fails to appear in Finder

Using the project from github I notice that saved documents do not show the txt icon.
I’m on OS X 10.10.3, xCode 6.3.1

This is a common issue which we believe is due to how Finder caches icons. Sometimes it takes a while for Finder to catch the updated icon. Unfortunately we do not have a clean work-around. You might try searching the web on “clear finder icon cache” and trying out the solutions proposed there. For example:

One thing to watch out for: if you have extra builds sitting around, which can happen if you are duplicating the project folder between chapters, you may inadvertently have another without document icons, which prevents Finder from updating to show the icons from your new version. You can get rid of those extra builds by using Build -> Clean in each project, or by removing the related folders within Xcode’s DerivedData folder, ~/Library/Developer/Xcode/DerivedData/.