It looks the project-description-setter plugin isn't compatible with the pipeline plugin, tried to add the following to my pipeline

writeFile file: 'project_description.txt', text: '''
testing
'''}
step([$class: 'project-description-setter ', filename: 'project_description.txt'])

This results in

java.lang.UnsupportedOperationException: no known implementation of interface jenkins.tasks.SimpleBuildStep is named project-description-setter

Would be nice if we could also do the following so that we don't need a filename

step([$class: 'project-description-setter ', text: 'foo'])

See https://github.com/jenkinsci/pipeline-plugin/blob/master/DEVGUIDE.md