Update the INSTALL file and related ones
Added "- khelpcenter KDE help viewer" so that pressing F1 shows Krusader's help. More information can be seen on https://bugs.kde.org/show_bug.cgi?id=399735#c6
In "https://invent.kde.org/utilities/krusader.git" the ".git" was removed in order to avoid "server certificate verification failed. CAfile: none CRLfile: none" errors in a huge network.
Revision: !32 (merged)