newServicePath(): Docs say add prefix but it's actually suffix

Summary:
In newServicePath() when a service with the suggestedName already exists
a suffix is added. Make the docs clearer on that point.

Reviewers: Frameworks, dfaure, apol

Reviewed By: dfaure

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D28530