Update docs README.md (apache#5895)

docs/README.md

@@ -69,6 +69,9 @@ If you are already familiar with SkyWalking, you could use this catalog to find
   * Service Mesh
     * [SkyWalking on Istio](en/setup/istio/README.md). Introduces how to use Istio Mixer bypass Adapter to work with SkyWalking.
     * Use [ALS (access log service)](https://www.envoyproxy.io/docs/envoy/latest/api-v2/service/accesslog/v2/als.proto) to observe service mesh, without Mixer. Follow [document](en/setup/envoy/als_setting.md) to open it.
+  * Proxy
+    * [Envoy Proxy](https://www.envoyproxy.io/)
+      * [Sending metrics to Skywalking from Envoy](en/setup/envoy/metrics_service_setting.md). How to send metrics from Envoy to SkyWalking using [Metrics service](https://www.envoyproxy.io/docs/envoy/latest/api-v2/config/metrics/v2/metrics_service.proto.html).
   * [Backend, UI and CLI setup document](en/setup/backend/backend-ui-setup.md).
     * [Backend setup document](en/setup/backend/backend-setup.md).
       * [Configuration Vocabulary](en/setup/backend/configuration-vocabulary.md). Configuration Vocabulary lists all available configurations provided by `application.yml`.
@@ -89,6 +92,11 @@ If you are already familiar with SkyWalking, you could use this catalog to find
       * [Time To Live (TTL)](en/setup/backend/ttl.md). Metrics and traces are time series data, they would be saved forever, you could set the expired time for each dimension.
       * [Dynamic Configuration](en/setup/backend/dynamic-config.md). Make configuration of OAP changed dynamic, from remote service or 3rd party configuration management system.
       * [Uninstrumented Gateways](en/setup/backend/uninstrumented-gateways.md). Configure gateways/proxies that are not supported by SkyWalking agent plugins, to reflect the delegation in topology graph.
+      * [Apdex threshold](en/setup/backend/apdex-threshold.md). Configure the thresholds for different services if Apdex calculation is activated in the OAL.
+      * [Service Grouping](en/setup/backend/service-auto-grouping.md). An automatic grouping mechanism for all services based on name.
+      * [Group Parameterized Endpoints](en/setup/backend/endpoint-grouping-rules.md). Configure the grouping rules for parameterized endpoints, to improve the meaning of the metrics.
+      * [Meter Analysis](en/setup/backend/backend-meter.md). Set up the backend analysis rules, when use [SkyWalking Meter System Toolkit](en/setup/service-agent/java-agent/README.md#advanced-features) or meter plugins. 
+      * [Spring Sleuth Metrics Analysis](en/setup/backend/spring-sleuth-setup.md). Configure the agent and backend to receiver metrics from micrometer. 
     * [UI setup document](en/setup/backend/ui-setup.md).
     * [CLI setup document](https://github.com/apache/skywalking-cli).
 * [UI Introduction](en/ui/README.md). Introduce the UI usage and features.