Update how_to_guides.rst (#1893)

Adding OpenSearch examples

docs/modules/indexes/how_to_guides.rst

@@ -46,6 +46,8 @@ In the below guides, we cover different types of vectorstores and how to use the
 
 `Milvus <./vectorstore_examples/milvus.html>`_: A walkthrough of how to use the Milvus vectorstore wrapper.
 
+`Open Search <./vectorstore_examples/opensearch.html>`_: A walkthrough of how to use the OpenSearch wrapper.
+
 `Pinecone <./vectorstore_examples/pinecone.html>`_: A walkthrough of how to use the Pinecone vectorstore wrapper.
 
 `Qdrant <./vectorstore_examples/qdrant.html>`_: A walkthrough of how to use the Qdrant vectorstore wrapper.
@@ -96,4 +98,4 @@ The examples here are all end-to-end chains that use indexes or utils covered ab
    :name: chains
    :hidden:
 
-   ./chain_examples/*
+   ./chain_examples/*