There's no problem in asking and answering your own question. The thing is that most users probably arrive here from Google when asking questions so a sort of separate wiki is not as useful as separate questions. The guys at Stack Overflow are actually experimenting with creating documentation (http://stackoverflow.com/documentation) that is slightly different than questions but is still community created and curated, but I think that's only available there.
If you do create your own questions and answer them, be ready for people to give answers that might be better than yours. Also be ready to access that your question might not be interesting. If you just cram a ton of information in a question and answer it will be confusing and too broad. It might even be closed for not being a good question.
One easy way to gather all "documentation" will be to create a
documentation tag. That way all questions asking for reading material can be grouped together.