TrenchBroom is not yet usable for Unvanquished, but if you're a developer you can be interested in the game file for testing purpose.
Download the game directory and put it in app/resources/games/ directory within TrenchBroom one.
Set the engine path in TrenchBroom preferences.
Unvanquished has advanced file layout for maps and resources. Every map resides in separate .dpk.
Filename must obey the rule: map-<mapname>_<mapversion>.dpk, eg. map-station_4.dpk.
Those are usually stored in a pkg directory, or a src directory when working with asset sources.