Add a link to the CppNorth announcement video. (#1581)

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

README.md

@@ -13,6 +13,9 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   <a href="#join-us">Join us</a>
 </p>
 
+**See our [announcement video](https://youtu.be/omrY53kbVoA) from
+[CppNorth](https://cppnorth.ca/)**
+
 <a href="docs/images/snippets.md#quicksort">
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