update docs for query rewriting

Author: mattgotteiner

docs/deploy_features.md

@@ -17,6 +17,7 @@ You should typically enable these features before running `azd up`. Once you've
 * [Enabling login and document level access control](#enabling-login-and-document-level-access-control)
 * [Enabling user document upload](#enabling-user-document-upload)
 * [Enabling CORS for an alternate frontend](#enabling-cors-for-an-alternate-frontend)
+* [Enabling query rewriting](#enabling-query-rewriting)
 * [Adding an OpenAI load balancer](#adding-an-openai-load-balancer)
 * [Deploying with private endpoints](#deploying-with-private-endpoints)
 * [Using local parsers](#using-local-parsers)
@@ -321,6 +322,13 @@ For an alternate frontend that's written in Web Components and deployed to Stati
 on [using a different backend](https://github.com/Azure-Samples/azure-search-openai-javascript#using-a-different-backend).
 Both these repositories adhere to the same [HTTP protocol for AI chat apps](https://aka.ms/chatprotocol).
 
+## Enabling query rewriting
+
+By default, [query rewriting](https://learn.microsoft.com/azure/search/semantic-how-to-query-rewrite) from the search service is not enabled. To enable query rewriting, set the following environment variables:
+
+1. Ensure semantic ranker is enabled. Query rewriting may only be used with semantic ranker. Run `azd env set AZURE_SEARCH_SEMANTIC_RANKER free` or `azd env set AZURE_SEARCH_SEMANTIC_RANKER standard` depending on your desired [semantic ranker tier](https://learn.microsoft.com/azure/search/semantic-how-to-configure).
+1. Enable query rewriting. Run `azd env set AUZRE_SEARCH_QUERY_REWRITING true`. An option in developer settings will appear allowing you to toggle query rewriting on and off. It will be on by default.
+
 ## Adding an OpenAI load balancer
 
 As discussed in more details in our [productionizing guide](./productionizing.md), you may want to consider implementing a load balancer between OpenAI instances if you are consistently going over the TPM limit.