Add instructions how patchset level comments can be disabled

Change-Id: I1456702b323b80eca63904422fe9419f90ad636f
diff --git a/pages/site/releases/3.3.md b/pages/site/releases/3.3.md
index 7c9918d..0f6d4dd 100644
--- a/pages/site/releases/3.3.md
+++ b/pages/site/releases/3.3.md
@@ -195,7 +195,15 @@
   Enabled by default.
   The former assignee feature is therefore now disabled by default.
 
-* Reply dialog posts patchset level comments instead of change messages.
+* The reply dialog posts patchset level comments instead of change messages.
+
+  This is an experiment that is enabled by default. However, it can be
+  disabled by adding 'UiFeature__patchset_comments' as disabled key in
+  [experiments section of gerrit.config](https://gerrit-review.googlesource.com/Documentation/config-gerrit.html#experiments).
+  This is useful if your CI system parses back change messages (e.g.
+  "/rerun") and has not been updated yet to parse patchset level
+  comments. The option to revert this behavior will be removed in
+  Gerrit 3.4. Until then, administrators need to have migrated.
 
 * [Issue 13670](https://bugs.chromium.org/p/gerrit/issues/detail?id=13670);
   Introduce cache.openFiles setting in gerrit.config.