Add a warning message to the main CMakeLists.txt about kde players.
Add a warning message to the main CMakeLists.txt about kde players.

KDE/gluon,pranavrc/example-gluon,KDE/gluon,pranavrc/example-gluon,pranavrc/example-gluon,KDE/gluon,KDE/gluon,pranavrc/example-gluon