Qt Concurrent has no documentation

This is for Qt Concurrent, but since there is no Qt Concurrent component, I am assigning this to Threads.

For each module, they need:

-landing page
-list of C++ classes (using the \module command)
-list of QML types (using the \qmlmodule command) if applicable
-page which lists examples (applicable for modules with many examples)

The work and status are kept here: http://qt-project.org/wiki/Qt5DocumentationProject

See the linked bug.