Use a parallel process event that instantly (0 frames transition time) tints the screen black. Now, there you go. Make a nice intro with some talking, music, credits, legends, etc. and/or whatever comes to your mind. You can just continue using this parallel process event.
Don't use auto-start in this case, because parallel process starts working as soon as you open the map while auto-start waits until the usual transition is over before it starts processing. If this confuses you, just try it out how it will work as auto-start and you will see what I mean.