Brainstorming a "Simple" Design Doc

I'm a little disappointed by the cancellation of the individual project, but mostly, it's a relief.  I was very concerned about my ability to devote an appropriate amount to time to it.  But Space Invaders -- now that can be done.

So now we need a game design document .  Normally, that's the first step in any game project, but in this case, a standard game design document seems almost like overkill for a game like this.  The question is, what sections would be appropriate to be in a design document for as simple a game as Space Invaders?  I'm going to brainstorm here 'cause it's a good place to keep a record of my thoughts.

• Overview
• Rules and Objectives
• Game Play Overview
• Victory/Loss Conditions
• Scoring
• User Interface and Controls
• Key Commands
• HUD Elements
• Multimedia Assets
• Graphics
• Audio