docs-rst: replace the selection.png by a SVG image

bitmap images don't scale too well. So, replace it by a SVG
image, written in inkscape. I'm using the 2009's temporary
logo.svg image from 8032b526

 ("linux.conf.au 2009: Tuz"),
with a Tasmanian Devil wearing a tux mask.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>