Update tracing README

Author: tillkruss

src/Psr/Tracing/README.md

@@ -4,3 +4,19 @@ A PSR-22 compatible tracing layer for Relay.
 
 - https://github.com/php-fig/fig-standards/blob/master/proposed/tracing.md
 - https://github.com/php-fig/fig-standards/blob/master/proposed/tracing-meta.md
+
+## Usage
+
+```php
+// connect to server
+$relay = new Relay(host: '127.0.0.1', port: 6379);
+
+// use global trace provider
+$client = RelayOpenTelemetry($client);
+
+// use custom trace provider
+$client = RelayOpenTelemetry($client, $tracerProvider);
+
+// use as regular
+$users = $relay->get('users:count');
+```