Warn or Prevent someone from trying to select track02 as CDDA

[Sappharad]

Per the instructions, you're only supposed to select tracks 4 and onward if rebuilding a disc with CDDA because GDIbuilder only cares about the high density (DC) area of the disc.

Users who aren't familiar with how this works can accidentally try to build with track 2 as one of their CDDA tracks. Do something to discourage this mistake from being made.