Added a few notes to the mdi example compositor regarding GL.
Added a few notes to the mdi example compositor regarding GL.

Tofee/qtwayland,ntanibata/qtwayland,locusf/qtwayland-1,ntanibata/qtwayland,locusf/qtwayland-1,ntanibata/qtwayland,Tofee/qtwayland,locusf/qtwayland-1,Tofee/qtwayland,locusf/qtwayland-1