Let me tell you a story. Early in my tenure at Yahoo we tried to get into the site dev process in the early stages in order to work SEO into the Product Recommendations Documents (PRD) before wireframing began. But as a fairly new horizontal group not reporting into any of the products, this was often difficult. Nay, damn near impossible. So usually we made friends with the product teams and got in where we could.
See the screenshot below for some of the sections for specific recommendations that you can add which will provide the meat of the document. Keep in mind this is a very flexible document – add recommendations that make sense (for example you may not always have specific design considerations for a project). Remember, it will be different every time you do it.