config-gerrit: Document the supported Elasticsearch version

Change-Id: I9c6646d5b9524bb553ccaef15eb60114568e8a79
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 3b9fae0..9ae0dc2 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -2791,8 +2791,8 @@
 [[elasticsearch]]
 === Section elasticsearch
 
-WARNING: The Elasticsearch support is incomplete. Online reindexing
-is still considered as beta.
+WARNING: The Elasticsearch support has only been tested with Elasticsearch
+version 2.4.x. Support for other versions is not guaranteed.
 
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 into types 'open_changes' and 'closed_changes' respectively.