add background info to README.md
add background info to README.md

adriaanm/scala-jenkins-infra,retronym/scala-jenkins-infra,scala/scala-jenkins-infra,lrytz/scala-jenkins-infra,retronym/scala-jenkins-infra,lrytz/scala-jenkins-infra,scala/scala-jenkins-infra,retronym/scala-jenkins-infra,adriaanm/scala-jenkins-infra,adriaanm/scala-jenkins-infra,lrytz/scala-jenkins-infra