[cairo] cairomm documentation patch

[Jonathon Jongsma]

Christopher Harvey wrote:
> Hi,
> I recently got pretty confused about why my program was crashing when I used 
> the rel_move_to and rel_line_to functions. I thought maybe some extra 
> documentation would have been nice. I attached a patch that warns about the 
> rel_ functions and the exceptions they can generate, hopefully helping others 
> in the future. This is a documentation change only.
> 
> -Chris

Thanks Chris,
I've pushed your patch to master.

-- 
jonner