docs: add SVG version of the Linux logo

docs: add SVG version of the Linux logo

In the Rust for Linux patch series, Jonathan Corbet requested [1] that
we avoid binary assets (such as the logo), possibly by recreating
them in SVG format.

However, it turns out there is no SVG version of the Linux logo
in the kernel tree yet, only a GIF one from the pre-v2.0.0 days.

This patch fixes that by adding a SVG version of the Linux logo,
which we could then use in the Rust for Linux documentation and
other similar places.

This is a vector re-illustration by Garrett LeSage of the original
logo by Larry Ewing, plus cleanups by IFo Hancroft.

The file was imported as-is from:

    https://github.com/garrett/Tux/blob/ecd40de64250ea2b24c849e901c3297ad01e54f6/tux.svg

The stated license in the repository is:

> Public domain http://creativecommons.org/publicdomain/zero/1.0/
>
> ...but, if anyone asks:
>
> Tux was originally made by Larry Ewing in the Gimp, re-illustrated
> in vector by Garrett LeSage, using Inkscape and refined and
> cleaned up by IFo Hancroft.

Here, the acknowledgement requirement has been made mandatory to
match the wording of the existing GIF logo in `COPYING-logo`.

Both Garrett LeSage and IFo Hancroft gave their permission [2,3]
to use their re-illustration with the license as given in
the `COPYING-logo` file.

Link: https://lore.kernel.org/lkml/87fspk1xoc.fsf@meer.lwn.net/
Link: https://lore.kernel.org/lkml/YgFsD7zBZyVqyF+F@battlestation/
Link: https://lore.kernel.org/lkml/CAFfNkxV=DmRJL1Oqm3w9YzBYcNLSAG3Ss8pih9ZVwh_E-Fbw+Q@mail.gmail.com/
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20220528153132.8636-2-ojeda@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>