Update README.md (DataDog#2760)

Requesting the following change be made from step 3 to use the updated statsd syntax in accordance with Grafana/k6's official documentation: https://grafana.com/docs/k6/latest/results-output/real-time/statsd/

Author: alexs-github-account

k6/README.md

@@ -48,7 +48,7 @@ For the detailed instructions, follow the [k6 documentation][2].
     Once the Datadog Agent service is running, run the k6 test and send the metrics to the Agent with:
 
     ```shell
-    K6_STATSD_ENABLE_TAGS=true k6 run --out xk6-output-statsd script.js
+    K6_STATSD_ENABLE_TAGS=true k6 run --out output-statsd script.js
     ```
 
 4. Visualize the k6 metrics in Datadog.