Add Documents to the default list of Places
This adds Documents to the default list of Places, as discussed with
general favor in D10245. This adds a common XDG directory that is often
used by users, making it easier and faster by default to access files.
Created a new user and observed and clicked on Documents, and the other
default places locations.
Reviewed By: Dolphin, ngraham
Subscribers: davidc, elvisangelaccio, kde-frameworks-devel, ngraham
Maniphest Tasks: T8349
Differential Revision: https://phabricator.kde.org/D16852