I'm not sure documentation per se is going to be useful. As Nick has noted reading documentation is something that many of our incoming users ("Ardueenies") are averse to doing.
Another thing they seem averse to doing is searching. The number of duplicate questions we get seems to be rather high. So instead of spending our time on documentation, it may be better to put our efforts into crafting "FAQ" questions where we cover, in detail, a specific topic. Then when we get a question that asks what that FAQ question covers we just close it as a duplicate pointing to the FAQ question.
This has proved successful on EE, especially for the question "What power supply do I want" or "Will my power supply blow up my project because of too many amps" and similar that seem to get asked about every 15 minutes. They all get almost immediately closed as a duplicate of "Choosing power supply, how to get the voltage and current ratings?"
Questions that people ask all the time that could be covered by this kind of thing (please suggest more):
- I have added a shield that has pins in all the Arduino's holes. Can I still use some of them?
- Can I run my Arduino of XXX power supply?
- Can I use an external power supply for my Arduino and still plug it into the USB? Will it blow up?
- How do you merge two k0d3z together? Will do you it for me? plz?
- How do I communicate between my Arduino and my PC / a Website / Neptune?
- What is the extra 6 pin header for on the Uno R3?
The list could go on for miles I am sure. Building up a store of these good quality in-depth answers would not only make life easier on us, since we would have to write less answers in the long run, but also would help the people asking the questions as they then get handed a well crafted, well thought out, detailed answer to their question instead of a half-arsed answer that we can't be bothered to flesh out because the same question has been asked time and time again and if only they'd spend the time doing a little searching, reading, and thinking about what they have found they would come up with the answer themselves.