[DOCS] Expands semantic_text docs with new ELSER endpoint

docs/reference/elasticsearch/mapping-reference/semantic-text.md

@@ -37,6 +37,14 @@ the embedding generation, indexing, and query to use.
 [quantized](/reference/elasticsearch/mapping-reference/dense-vector.md#dense-vector-quantization)
 to `bbq_hnsw` automatically.
 
+## Default and custom endpoints
+
+You can use either preconfigured endpoints in your `semantic_text` fields which
+are ideal for most use cases or create custom endpoints and reference them in
+the field mappings.
+
+### Using the default ELSER endpoint
+
 If you use the preconfigured `.elser-2-elasticsearch` endpoint, you can set up
 `semantic_text` with the following API request:
 
@@ -53,6 +61,8 @@ PUT my-index-000001
 }
 ```
 
+### Using a custom endpoint
+
 To use a custom {{infer}} endpoint instead of the default
 `.elser-2-elasticsearch`, you
 must [Create {{infer}} API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-inference-put)
@@ -96,6 +106,35 @@ PUT my-index-000003
 }
 ```
 
+### Using ELSER on EIS
+
+```{applies_to}
+stack: preview 9.1
+serverless: preview
+```
+
+If you use the preconfigured `.elser-2-elastic` endpoint that utilizes the ELSER model as a service through the Elastic Inference Service ([ELSER on EIS](docs-content://explore-analyze/elastic-inference/eis.md#elser-on-eis)), you can
+set up `semantic_text` with the following API request:
+
+```console
+PUT my-index-000001
+{
+  "mappings": {
+    "properties": {
+      "inference_field": {
+        "type": "semantic_text",
+        "inference_id": ".elser-2-elastic"
+      }
+    }
+  }
+}
+```
+
+::::{note}
+While we do encourage experimentation, we do not recommend implementing production use cases on top of this feature while it is in Technical Preview.
+
+::::
+
 ## Parameters for `semantic_text` fields [semantic-text-params]
 
 `inference_id`