Add CompositionGraphicsDevice exception remark

Author: trympet

windows.ui.composition/compositiongraphicsdevice_createdrawingsurface2_1137892861.md

@@ -29,6 +29,7 @@ The alpha mode of the drawing surface.
 Returns the created CompositionDrawingSurface.
 
 ## -remarks
+If the requested pixel format is unsupported by the graphics device, an exception will be thrown.
 
 ## -see-also