Updating README

Author: LikeTheSalad

opamp-client/README.md

@@ -3,6 +3,56 @@
 Java implementation of the OpAMP
 client [spec](https://github.com/open-telemetry/opamp-spec/blob/main/specification.md).
 
+> [!WARNING]
+> This is an incubating feature. Breaking changes can happen on a new release without previous
+> notice and without backward compatibility guarantees.
+
+## Usage
+
+```java
+// Initializing it
+
+RequestService requestService = HttpRequestService.create(OkHttpSender.create("[OPAMP_SERVICE_URL]"));
+// RequestService requestService = WebSocketRequestService.create(OkHttpWebSocket.create("[OPAMP_SERVICE_URL]")); // Use this instead to connect to the server via WebSocket.
+OpampClient client =
+    OpampClient.builder()
+        .putIdentifyingAttribute("service.name", "My service name")
+        .enableRemoteConfig()
+        .setRequestService(requestService)
+        .build(
+            new OpampClient.Callbacks() {
+              @Override
+              public void onConnect() {}
+
+              @Override
+              public void onConnectFailed(@Nullable Throwable throwable) {}
+
+              @Override
+              public void onErrorResponse(ServerErrorResponse errorResponse) {}
+
+              @Override
+              public void onMessage(MessageData messageData) {
+                AgentRemoteConfig remoteConfig = messageData.getRemoteConfig();
+                if (remoteConfig != null) {
+                  // A remote config was received
+
+                  // After applying it...
+                  client.setRemoteConfigStatus(
+                      new RemoteConfigStatus.Builder()
+                          .status(RemoteConfigStatuses.RemoteConfigStatuses_APPLIED)
+                          .build());
+                }
+              }
+            });
+
+// State update
+client.setAgentDescription(new AgentDescription.Builder().build());
+
+// App shutdown
+client.close();
+
+```
+
 ## Component owners
 
 - [Cesar Munoz](https://github.com/LikeTheSalad), Elastic