Add some extra explanations on how to run tests in the dev readme

DEV.md

@@ -43,7 +43,8 @@ Filter test suites with
 ./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.Multiple scripts'
 ```
 
-Pass the `--debug` option to debug integration tests:
+You can pass the `--debug` option to debug Scala CLI when running integration tests. Note that this allows to debug the
+Scala CLI launcher (the app) and not the integration test code itself. The debugger is being run in the `attach` mode.
 
 ```bash
 ./mill integration.test.jvm 'scala.cli.integration.RunTestsDefault.*' --debug
@@ -61,6 +62,7 @@ The debug option uses 5005 port by default. It is possible to change it as follo
 
 ```bash
 ./mill integration.test.native
+./mill integration.test.native 'scala.cli.integration.RunTestsDefault.*'
 ```
 
 #### Generate native packages