mirror: Add logo to README.md

Let's display the brand new logo on bpftool's README.md. We can also
remove the level-1 heading from the README.md, to avoid a duplicate
title.

Add a link to the assets directory so that users can easily look up at
the logo's context in the associated README.md. Wrap the image in a
<div> so that the link spans on the full width of the column.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>

README.md

@@ -1,8 +1,14 @@
-bpftool
+<a href=".github/assets/">
+  <div>
+    <img src=".github/assets/bpftool_horizontal_color.svg"
+         alt="bpftool logo: Hannah the Honeyguide"
+         width=500px; />
+  </div>
+</a>
+
 [![License BSD 2-Clause][bsd-badge]](LICENSE.BSD-2-Clause)
 [![License GPL 2.0][gpl-badge]](LICENSE.GPL-2.0)
 [![Build status][build-badge]][build]
-=======
 
 [bsd-badge]: https://img.shields.io/badge/License-BSD_2--Clause-blue.svg
 [gpl-badge]: https://img.shields.io/badge/License-GPL_2.0-blue.svg