docs: Add release notes and NEWS item for 9.2.1 release

Better late than never, right?
diff --git a/docs/index.html b/docs/index.html
index 2f04335..6470503 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -16,6 +16,13 @@
 
 <h1>News</h1>
 
+<h2>October 4, 2013</h2>
+<p>
+<a href="relnotes/9.2.1.html">Mesa 9.2.1</a> is released.
+This is a new development release.
+See the release notes for more information about the release.
+</p>
+
 <h2>August 27, 2013</h2>
 <p>
 <a href="relnotes/9.2.html">Mesa 9.2</a> is released.