Correct help link for the new versions of KF5 (>52)

Summary:
Due to me "broken" KHelpClient in KF 5.52, links in the help menu show error messages now.

BUG: 402837

Test Plan:
1. Start KPat.
2. Select Freecell.
3. On the menubar, select "Help -> Help with Freecell".
4. Help for Freecell should be shown.

Reviewers: #kde_games, aacid, ltoscano

Reviewed By: ltoscano

Subscribers: ltoscano, kde-games-devel

Differential Revision: https://phabricator.kde.org/D17953