In Qt 4, each release has a single file that covers all of Qt. This file lives in dist/changes-4.x.y (along with all the historical changes files for previous versions). The current changes file is moved to the root directory in source packages.
For Qt 5, the previously stated intention was to have a changes-5.x.y file for each module. So far, there are only two changes-5.0.0 files (in qtbase/dist/changes-5.0.0 and qtqa/dist/changes-5.0.0).
The missing files for other modules need to be produced (and the two existing ones are probably incomplete) and a decision needs to be made about how these are presented to the user in packages.
For example, the changes files could be merged together, copied to the package root as changes-<module>-5.0.0, or the information could be merged into the regular Qt product docs instead of living in separate text files.