docs: elasticsearch docs for materializing keywords

site/docs/reference/Connectors/materialization-connectors/Elasticsearch.md

@@ -22,7 +22,6 @@ To use this connector, you'll need:
 If you haven't yet captured your data from its external source, start at the beginning of the [guide to create a dataflow](../../../guides/create-dataflow.md). You'll be referred back to this connector-specific documentation at the appropriate steps.
 :::
 
-
 ## Configuration
 
 To use this connector, begin with data in one or more Flow collections.
@@ -94,6 +93,43 @@ This connector supports both standard and delta updates. You must choose an opti
 
 [Learn more about delta updates](../../../concepts/materialization.md#delta-updates) and the implications of using each update type.
 
+## Keyword Fields
+
+Collection fields with `type: string` will have `keyword` index mappings created for them if they
+are part of the collection key, and `text` mappings for them if they are not part of the collection
+key.
+
+To materialize a collection field with `type: string` as a `keyword` mapping instead of a `text`
+mapping, configure the [field selection](../../../concepts/materialization.md#projected-fields) for
+the binding to indicate which fields should having keyword mappings created for them using the key
+and value of `"keyword": true`. This can be changed by updating the JSON in the **Advanced
+Specification Editor** in the web app or by using `flowctl` to edit the specification directly, see
+[edit a materialization](../../../guides/edit-data-flows.md#edit-a-materialization) for more details.
+
+An example JSON configuration for a binding that materializes `stringField` as a `keyword` mapping
+is shown below:
+
+```json
+{
+  "bindings": [
+    {
+      "resource": {
+        "index": "my-elasticsearch-index",
+      },
+      "source": "PREFIX/source_collection",
+      "fields": {
+        "include": {
+          "stringField": {
+            "keyword": true
+          }
+        },
+        "recommended": true
+      }
+    }
+  ]
+}
+```
+
 ## Changelog
 
 The changelog includes a list of breaking changes made to this connector. Backwards-compatible changes are not listed.