Update 2.16.4 release notes with new fix for PolyGerrit

This mention a fix for the inline editor (PolyGerrit).

Change-Id: I4868739a71c0898d3d7fd7910eadce53a195eedd
diff --git a/pages/site/releases/2.16.md b/pages/site/releases/2.16.md
index 35ec75e..07516c4 100644
--- a/pages/site/releases/2.16.md
+++ b/pages/site/releases/2.16.md
@@ -520,6 +520,10 @@
 
 #### PolyGerrit
 
+* [Issue 10371](https://bugs.chromium.org/p/gerrit/issues/detail?id=10371):
+  Fix an issue where a saved edit would always restore the same content
+  in subsequent edits of the same file, due to the cache not being erased.
+
 * [Issue 9909](https://bugs.chromium.org/p/gerrit/issues/detail?id=9909):
   Do not crash PolyGerrit UI if permitted labels array is empty