Add Lit 2 release livestream post (#511)

* Add Lit 2 release livestream post.

* Fix typos.

Author: Arthur Evans

packages/lit-dev-content/site/blog/2021-09-22-lit-2-release-livestream.md

@@ -0,0 +1,15 @@
+---
+tags: blogPosts
+layout: blog-post.html
+title: "Watch the Lit 2 release livestream"
+summary: "What's new in Lit 2, a big-picture view of Lit usage at Google, and a community panel discussion."
+date: 2021-09-22
+---
+
+<div class="preamble">
+
+If you weren't able to join us for the Lit 2  release livestream, you can watch the recording on YouTube.
+
+<iframe width="560" height="315" src="https://www.youtube-nocookie.com/embed/nfb779XIhsU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+
+</div>