(2-4 sentences explaining the project)
(bullet list describing the problem being solved)
(bullet list describing the limits of the project)
(terminology and history one needs to know to understand the design)
(a brief, high-level description of the design; diagrams are helpful)
(the design in detail; usually a top-down description)
(alternatives considered and rejected)
(security/privacy ramifications and how those concerns are mitigated)
(questions regarding requirements, mockups, etc)