Update the "About KDE" text

Summary: This text had not been updated in a while, and mentioned "workspaces" as a product line. Let's bring it up to date.

Test Plan:

Reviewers: VDG, Plasma, Frameworks, KDE Applications, KDE Promo

Reviewed By: KDE Promo

Subscribers: valorie, davidc, xyquadrat, rizzitello, ltoscano, aspotashev, abetts, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D16395