docs: setting up cross cluster search (#12599)

There isn't a whole lot to say about cross cluster search support in
Kibana other than how to set it up, which is by design.

docs/management/index-patterns.asciidoc

@@ -81,4 +81,6 @@ To delete an index pattern:
 . Go to the *Settings > Indices* tab.
 . Select the pattern you want to remove in the Index Patterns list.
 . Click the pattern's *Delete* button.
-. Confirm that you want to remove the index pattern.
+. Confirm that you want to remove the index pattern.
+
+include::index-patterns/management-cross-cluster-search.asciidoc[]

docs/management/index-patterns/management-cross-cluster-search.asciidoc

@@ -0,0 +1,33 @@
+[[management-cross-cluster-search]]
+=== Cross Cluster Search
+
+beta[]
+
+Elasticsearch supports the ability to run search and aggregation requests across multiple
+clusters using a module called _cross cluster search_.
+
+In order to take advantage of cross cluster search, you must configure your Elasticsearch
+clusters accordingly. Review the corresponding Elasticsearch
+{ref}/modules-cross-cluster-search.html[documentation] before attempting to use cross cluster
+search in Kibana.
+
+Once your Elasticsearch clusters are configured for cross cluster search, you can create
+specific index patterns in Kibana to search across the clusters of your choosing. Using the
+same syntax that you'd use in a raw cross cluster search request in Elasticsearch, create your
+index pattern in Kibana with the convention `<cluster-names>:<pattern>`.
+
+For example, if you want to query logstash indices across two of the Elasticsearch clusters
+that you set up for cross cluster search, which were named `cluster_one` and `cluster_two`,
+you would use `cluster_one,cluster_two:logstash-*` as your index pattern in Kibana.
+
+Just like in raw search requests in Elasticsearch, you can use wildcards in your cluster names
+to match any number of clusters, so if you wanted to search logstash indices across any
+clusters named `cluster_foo`, `cluster_bar`, and so on, you would use `cluster_*:logstash-*`
+as your index pattern in Kibana.
+
+If you want to query across all Elasticsearch clusters that have been configured for cross
+cluster search, then use a standalone wildcard for your cluster name in your Kibana index
+pattern: `*:logstash-*`.
+
+Once an index pattern is configured using the cross cluster search syntax, all searches and
+aggregations using that index pattern in Kibana take advantage of cross cluster search.

docs/setup/tribe.asciidoc

@@ -1,6 +1,11 @@
 [[tribe]]
 == Using Kibana with Tribe nodes
 
+NOTE: While tribe nodes have been deprecated in Elasticsearch in favor of
+<<management-cross-cluster-search>>, you can still use Kibana with tribe nodes until
+version 7.0. Unlike tribe nodes, using cross cluster search in Kibana requires no
+server-side configurations and doesn't disable functionality like <<console-kibana>>.
+
 Kibana can be configured to connect to a {ref}/modules-tribe.html[tribe node] for data retrieval.  Because tribe nodes can't create indices, Kibana additionally
 requires a separate connection to a node to maintain state.  When configured, searches and visualizations will retrieve data using
 the tribe node and administrative actions (such as saving a dashboard) will be sent to non-tribe node.