Update upgrade.html.md for breaking changes
diff --git a/docs/manual/source/resources/upgrade.html.md b/docs/manual/source/resources/upgrade.html.md
index f708fb8..2533c6d 100644
--- a/docs/manual/source/resources/upgrade.html.md
+++ b/docs/manual/source/resources/upgrade.html.md
@@ -36,6 +36,13 @@
In addition, please take notes of the following for specific version upgrade.
+## Upgrade to 0.12.0
+
+In 0.12.0, Elasticsearch 5.x client has been reimplemented as a singleton.
+Engine templates directly using Elasticsearch 5.x StorageClient require
+update for compatibility. See [pull request]
+(https://github.com/apache/incubator-predictionio/pull/421) for details.
+
## Upgrade to 0.11.0
Starting from 0.11.0, PredictionIO no longer bundles any JDBC drivers in the
