Add Tuple sponsorship banner to readme

Until December.

README.md

@@ -1,5 +1,16 @@
 <a id="top"></a>
-![Catch2 logo](data/artwork/catch2-logo-full-with-background.svg)
+
+<table width="100%">
+  <tr>
+    <td align="center" width="50%"><img src="/data/artwork/catch2-logo-full-with-background.svg" width="100%"></td>
+    <td align="center" width="50%">
+      <figure>
+        <figcaption>Special thanks to:</figcaption>
+        <a href="https://tuple.app/catch2"><img src="/data/sponsors/github_repo_sponsorship.png" width="100%"></a>
+      </figure>
+    </td>
+  </tr>
+</table>
 
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