Merge pull request quarkusio#15137 from geoand/step-time-doc

Clarify the usage of quarkus.debug.print-startup-times

docs/src/main/asciidoc/writing-extensions.adoc

@@ -1425,7 +1425,7 @@ convenience to avoid the need to explicitly load classes in the recorders.
 ==== Printing step execution time
 
 At times, it can be useful to know how the exact time each startup task (which is the result of each bytecode recording) takes when the application is run.
-The simplest way to determine this information is to set the `quarkus.debug.print-startup-times` property to `true` when running the application.
+The simplest way to determine this information is to launch the Quarkus application with the `-Dquarkus.debug.print-startup-times=true` system property.
 The output will look something like:
 
 [source%nowrap]
@@ -2992,4 +2992,4 @@ Finally, generate the documentation and check it out.
 In order to make it easy for extension authors to test their extensions daily against the latest snapshot of Quarkus, Quarkus has introduced
 the notion of Ecosystem CI. The Ecosystem CI link:https://github.com/quarkusio/quarkus-ecosystem-ci/blob/master/README.adoc[README]
 has all the details on how to set up a GitHub Actions job to take advantage of this capability, while this link:https://www.youtube.com/watch?v=VpbRA1n0hHQ[video] provides an overview
-of what the process looks like.
+of what the process looks like.