In terms of code I think github flow MOSTLY covers it, maybe just reiterate the key points: Branch -> PR (code review) -> Test -> merge -> deploy. 

In terms of process of dealing with clients maybe we have a small outline of the sales steps->contract example link (maybe we post the example contract here?) -> setting up trello or basecamp -> weekly goals/deliverables/meetings -> github flow -> ???

Maybe also cover the rules for internal projects?