add Standalone mode desc

Author: Foo Bar

CHANGELOG.md

@@ -71,6 +71,19 @@ Enable additional features not included in the standard Kubernetes Gateway API,
 
 * HTTPRoutePolicy: Configures advanced traffic management and routing policies for HTTPRoute or Ingress resources, enhancing functionality without modifying the original resources.
 
+**Support APISIX Standalone API-Driven Mode (Experimental)**
+
+> This mode is experimental, please do not rely on it in your production environment. We use it to validate certain specific workloads and if it is appropriate we will turn it into an officially supported feature, otherwise it will be removed.
+
+In this mode, there is no need to maintain an ETCD cluster. Routing rules are stored entirely in memory and can be updated through the API.
+
+You can enable this mode in Apache Ingress configuration file by specifying:
+
+```yaml
+provider:
+  type: "apisix-standalone"
+```
+
 ### Contributors
 
 * Ashing Zheng