Merge pull request #4925 from jwhitlock/es-docs-1464093

bug 1464093: Update ElasticSearch docs for 5.6.10

docs/elasticsearch.rst

@@ -7,15 +7,24 @@ Kuma uses Elasticsearch_ to power its on-site search.
 
 Installed version
 =================
-Elasticsearch `releases new versions often`_, and Kuma is slow to upgrade. The
-Docker environment uses 2.4, and production uses 1.7, with a planned update to 2.4.
+Elasticsearch `releases new versions often`_. They release a new minor version
+(for example, 6.2.0, 6.3.0) every 30 to 90 days, and support the most recent
+minor version. They release a major version (5.0.0, 6.0.0) every 12 to 18
+months, and support the last minor version of the previous major release
+(for example, 2.4.x supported until 6.x is released, 5.6.x supported until 7.x
+is released).
+
+Kuma's goal is to update to the last minor version of the previous major
+release, so we expect to update every 12 to 18 months. Kuma is running on
+ElasticSearch 5.6.10 in development and production, which is planned to be
+supported until March 2019.
 
 The Kuma search tests use the configured Elasticsearch, and can be run inside
 the ``web`` Docker container to confirm the engine works::
 
     py.test kuma/search/
 
-.. _releases new versions often: https://en.wikipedia.org/wiki/Elasticsearch#History
+.. _releases new versions often: https://www.elastic.co/support/eol
 
 .. _indexing-documents: