DOCSP-22866 clustered indexes (#234)

* added clustered indexes

Author: kyuan-mongodb

source/fundamentals/indexes.txt

@@ -397,6 +397,30 @@ Refer to the :manual:`Unique Indexes page </core/index-unique>` in the MongoDB s
 
 .. driver-content-end
 
+Clustered Indexes
+~~~~~~~~~~~~~~~~~
+
+**Clustered indexes** instruct a collection to store documents ordered
+by a key value. To create a clustered index, specify the clustered index
+option with the ``_id`` field as the key and the unique field as
+``true`` when you create your collection.
+
+The following example creates a clustered index on the ``_id`` field in
+the ``vendors`` collection:
+
+.. code-block:: java
+   
+   MongoDatabase database = mongoClient.getDatabase("tea");
+   ClusteredIndexOptions clusteredIndexOptions = new ClusteredIndexOptions(new Document("_id", 1), true);
+   CreateCollectionOptions createCollectionOptions = new CreateCollectionOptions().clusteredIndexOptions(clusteredIndexOptions);
+
+   database.createCollection("vendors", createCollectionOptions);
+
+See the MongoDB server manual sections for more information:
+
+- :ref:`Clustered Indexes <db.createCollection.clusteredIndex>`
+- :ref:`Clustered Collections <clustered-collections>`
+
 Remove an Index
 ---------------