This site should list license and author (according to the desired form of attribution) of every asset file that is shipped with the game inside the pak[…].pk3 files. Please make sure you keep this site up to date when you contribute assets. Maps, even those that are shipped with the game, have to maintain and ship their own comprehensive license files, preferably as a text file in an about directory inside the pk3.
If you are part of the development team, feel free to release your work in the name of "Unvanquished Development". You can add a note that explains that you are the author.
For each directory, add one entry for any number of files that has the same author. You can use * as a wildcard character for file names. Separate multiple files with space. When multiple patterns match, the one that is highest in the list wins.