Update 2.16.9 release notes

Change-Id: I13de991a8dcc361410ed1d15177ecbb61fe310fb
diff --git a/pages/site/releases/2.16.md b/pages/site/releases/2.16.md
index c3b0f7d..9ab30ef 100644
--- a/pages/site/releases/2.16.md
+++ b/pages/site/releases/2.16.md
@@ -548,6 +548,12 @@
 
 * PolyGerrit fixes
 
+  * [Issue 10670](https://bugs.chromium.org/p/gerrit/issues/detail?id=10670):
+  Fix selection of merge base when navigating between merge commit changes.
+
+    When navigating between merge commit changes, the selection of the merge
+    base was not persisted.
+
   * Hide overflowing author element content.
 
     In the case of vertical stacking unicode characters it was possible for