giochannel: Clarify type of GSource callback in documentation
This should clarify questions like https://stackoverflow.com/q/57807738/2931197.
Signed-off-by: Philip Withnall withnall@endlessm.com
This should clarify questions like https://stackoverflow.com/q/57807738/2931197.
Signed-off-by: Philip Withnall withnall@endlessm.com