Personally I've come to favor keeping the technical documentation close to the code. That is, keep it as markdown files and check it into git. They are just as easily hyperlinked to as a wiki page on the bitbucket web interface (or whichever system is used). The main README.md should contain information on how to set up the dev environment. Other README.md files, located in the folder root of modules, provide more specific information.

Documentation of a less technical nature may still find a natural home in the Wiki, since we also need a place where various managers, testers, salespeople, support people, etc. can maintain their documentation.