Add limitations to EEM docs (#4281)

* add eem limitations to serverless docs

* add eem limitations to stateful docs

Author: colleenmcginnis

docs/en/observability/elastic-entity-model.asciidoc

@@ -65,3 +65,11 @@ The following {es} privileges are required to delete {es} resources:
 |application: `kibana-.kibana`, privileges: [`saved_object:entity-definition/delete`, `saved_object:entity-discovery-api-key/delete`], resources: [*]
 |====
 
+[discrete]
+[[elastic-entity-model-limitations]]
+== Limitations
+
+* {ref}/modules-cross-cluster-search.html[Cross-cluster search (CCS)] is not supported.
+  EEM cannot leverage data stored on a remote cluster.
+* Services are only detected from documents where `service.name` is detected in index
+  patterns that match either `logs-*` or `apm-*`.

docs/en/serverless/elastic-entity-model.mdx

@@ -39,3 +39,8 @@ the Elastic Entity Model is enabled when you turn on the entity-centric service
 <Roles role="Admin" goal="enable the Elastic Entity Model" />
 
 From the Dev Console, run the command: `DELETE kbn:/internal/entities/managed/enablement`
+
+## Limitations
+
+* [Cross-cluster search (CCS)](https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-cross-cluster-search.html) is not supported. EEM cannot leverage data stored on a remote cluster.
+* Services are only detected from documents where `service.name` is detected in index patterns that match either `logs-*` or `apm-*`.