Update documentation for new P4_CHANGELIST behavior

(karl_wirth)
JENKINS-37584

SETUP.md

@@ -394,13 +394,6 @@ Use this snippet with your intended target e.g. a slave calles 'my_slave'

For more examples and usage please refer to the [Workflow docs](https://github.com/jenkinsci/workflow-plugin/blob/master/README.md).

### Workflow Limitations

There are several limitations as the Workflow plugin is relativly new, these include:

* SCM Polling (not functional)
* No access to Environment ${VAR} varables

### Exposed Variables

The plugin exposes the following additional variables:
@@ -412,6 +405,10 @@ The plugin exposes the following additional variables:
* *P4_TICKET* - Perforce ticket used (can be hidden using global configuration option 'Perforce: Secure P4_TICKET').
* *HUDSON_CHANGELOG_FILE* - Location on disk of 'changelog.xml' containing list of changes in this build.

For example in a Pipeline script you can use:

    ${env.P4_CHANGELIST}


## Troubleshooting