* move `searx/static/themes/simple/img/searxng.svg` to `src/brand/searxng.svg`
* README.rst can use it without a reference to a theme.
* the simple theme can create `searx/static/themes/simple/img/searxng.png` using
the svg2png task
Suggested-by: @dalf https://github.com/searxng/searxng/pull/561#issuecomment-981747902
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
