There were some questions and I personally struggled with it when I started with Impact - so here we go.
Check zipped file for the whole code as there are some issues when displaying the code.
Check the zip for the full source...
Its fairly simple add this at the end of your main.js before your canvas call.
Source/Support Files: TitlescreenSnippet.zip
Its fairly simple to achieve. The whole idea is to create additional class extension that will hold your intro screen and then just switch between them using ig.system.setGame() call.
To ensure consistency make sure stuff like score or lives is held in a global variable rather as an attribute of your game object as every time you change the to intro and then to game your data will be reset.