Add Wireguard logo (SVG) (#455)

* Added wireguard.svg.

* Added WireGuard icon to README.md.
Added reference image to images/reference/wireguard.svg and updated images/reference/index.md correspondingly.

* Corrected the Aria label for wireguard.svg. This added 5 bytes to the size; updated README.md correspondingly.

Co-authored-by: Terence Eden <edent@users.noreply.github.com>

images/reference/wireguard.svg

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8"?>
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