add "-l app=nginx" after "kubectl get pods"

the original sentence is "kubectl get pods", but maybe "kubectl get pods -l app=nginx" is more accurat in the context.
Please check for this.

docs/tutorials/stateless-application/run-stateless-application-deployment.md

@@ -101,7 +101,7 @@ should have four pods:
 
 1. Verify that the Deployment has four pods:
 
-        kubectl get pods
+        kubectl get pods -l app=nginx
 
     The output is similar to this: