Here are some things that work for documenting swift code in Xcode 6. It is very buggy and sensitive to colons, but it's better than nothing:
class Foo {
    /// This method does things.
    /// Here are the steps you should follow to use this method
    ///
    /// 1. Prepare your thing
    /// 2. Tell all your friends about the thing.
    /// 3. Call this method to do the thing.
    ///
    /// Here are some bullet points to remember
    ///
    /// * Do it right
    /// * Do it now
    /// * Don't run with scissors (unless it's tuesday)
    ///
    /// :param: name The name of the thing you want to do
    /// :returns: a message telling you we did the thing
    func doThing(name : String) -> String {
        return "Did the \(name) thing";
    }
}
The above is rendered in Quick Help as you would expect with formatted numeric lists, bullet points, parameter and return value documentation.
None of this is documented - file a Radar to help them along.