Explain re-triggering lid close on profile change

Summary:
This code was added for https://bugs.kde.org/show_bug.cgi?id=243618 but
the frameworks repo splitting makes the history hard to reach without
following https://community.kde.org/Frameworks/GitOldHistory to graft in
the old history.

So explain the motivation in the code comments. See
https://phabricator.kde.org/D2325 for more background.

Test Plan: Compiled

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D2934