provide information about caps in readme

lib/extensions/caps/README.markdown

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+# Entity Capabilities
+
+This extension provides support for handling capabilities in the XMPP protocol using Caps (short for **Capabilities**) feature. Allows a client to advertise its capabilities to other entities and discover the capabilities of other entities in the XMPP network.
+
+## Features
+
+- Advertise and discover capabilities of XMPP entities.
+- Efficiently handle capabilities updates to avoid unnecessary queries.
+- Automatic capabilities exchange during XMPP connection establishment.
+
+## Limitations
+
+Please note that you need to use `echo.disco.addFeature` and `echo.disco.addIdentity` methods to add capabilities features and identity to the client. This extension does not provide built-in methods for adding features and identities to the disco extension.
+
+## Embedding
+
+This extension comes built-in to the client. It means you do not need to attach this extension as you did on other extensions. You can not disable or enable this feature in any way.
+
+## API
+
+This code snippet demonstrates how to use this extension for the client.
+
+```dart
+
+import 'dart:async';
+import 'dart:developer';
+
+import 'package:echo/echo.dart';
+
+Future<void> main() async {
+  final echo = Echo(service: 'ws://example.com:5443/ws');
+
+  await echo.connect(
+    jid: 'vsevex@example.com',
+    password: 'randompasswordwhichisgoingtobeyourpassword',
+    callback: (status) async {
+      if (status == EchoStatus.connected) {
+        log('Connection Established');
+        echo.disco.addFeature('someFeature');
+        echo.caps.sendPresence();
+      } else if (status == EchoStatus.disconnected) {
+        log('Connection Terminated');
+      } else if (status == EchoStatus.register) {
+        registrationCompleter.complete(true);
+      }
+    },
+  );
+}
+
+```