fixes argoproj#12961. Add example of standard output of a step as out…

…put parameter

docs/walk-through/output-parameters.md

@@ -80,7 +80,7 @@ spec:
         template: print-message
         arguments:
           parameters:
-          # Pass the hello-param output from the generate-parameter step as the message input to print-message
+          # Pass the stdout from the generate-parameter step as the message input to print-message
           - name: message
             value: "{{steps.generate-parameter.outputs.result}}"
 
@@ -99,4 +99,4 @@ spec:
       image: docker/whalesay:latest
       command: [cowsay]
       args: ["{{inputs.parameters.message}}"]
-```
+```