Documents ELSER autoscale limitation (#2719)

* Documents ELSER autoscale limitation.

* Addresses feedback.

(cherry picked from commit 3487c6d)

docs/en/stack/ml/nlp/ml-nlp-limitations.asciidoc

@@ -17,4 +17,16 @@ When you use ELSER for semantic search, only the first 512 extracted tokens from
 each field of the ingested documents that ELSER is applied to are taken into 
 account for the search process. If your data set contains long documents, divide 
 them into smaller segments before ingestion if you need the full text to be 
-searchable.
+searchable.
+
+
+[discrete]
+[[ml-nlp-elser-autoscale]]
+== ELSER deployments don't autoscale
+
+Currently, ELSER deployments do not scale up and down automatically depending on
+the resource requirements of the ELSER processes. If you want to configure
+available resources for your ELSER deployments, you can manually set the number
+of allocations and threads per allocation by using the Trained Models UI in
+{kib} or the 
+{ref}/update-trained-model-deployment.html[Update trained model deployment API].