docs/website: add OpenWide/Smile as sponsor

docs/website: add OpenWide/Smile as sponsor

As mentionned in
http://lists.busybox.net/pipermail/buildroot/2016-July/167050.html,
OpenWide/Smile has sponsored the Buildroot Summer Camp, by allowing
Romain Naour to participate, and by paying the food expenses for the
event.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Jérémy Rosen <jeremy.rosen@smile.fr>
[Thomas:
 - renamed the logo file
 - remove useless white area in the logo, so that it appears bigger on
   the website]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>