Add a logo [NFC] (#8102)

Process:

* Take the Emscripten logo (seems fitting given the origin of this
  project)
* Change colors to the wasm logo's "royal blue"
* Mess around in Inkscape for a while to add a "B"

Someone with artistic talent could surely do better, of course...

Author: kripken

README.md

@@ -1,3 +1,10 @@
+<div align="center">
+  <a href="https://github.com/WebAssembly/binaryen">
+    <img src="media/logo.svg" width=300 alt="Binaryen logo"/>
+  </a>
+  <br>
+</div>
+
 [![CI](https://github.com/WebAssembly/binaryen/actions/workflows/ci.yml/badge.svg?branch=main&event=push)](https://github.com/WebAssembly/binaryen/actions/workflows/ci.yml?branch=main&event=push)
 
 # Binaryen