Elasticsearch: Mention support for Elasticsearch 7.0.x

Change-Id: If507f2b56b59840776fb59abcb8ca90b89892eec
diff --git a/pages/site/elasticsearch.md b/pages/site/elasticsearch.md
index 41e3700..3d24a60 100644
--- a/pages/site/elasticsearch.md
+++ b/pages/site/elasticsearch.md
@@ -19,3 +19,9 @@
 | 6.5.x                 | 2.15.8 or 2.16.1       |                                           |
 | 6.6.x                 | 2.15.10 or 2.16.5      |                                           |
 | 6.7.x                 | 2.15.13 or 2.16.8      |                                           |
+| 7.0.x                 | 2.15.13 or 2.16.8      | See note below about upgrades             |
+
+Indices created in Elasticsearch 5.x or earlier will need to be reindexed with
+Elasticsearch 6.x in order to be readable by Elasticsearch 7.x. See
+[breaking changes in Elasticsearch 7.0](https://www.elastic.co/guide/en/elasticsearch/reference/7.0/breaking-changes-7.0.html)
+for details.