Graphviz must be in the $PATH.
In project/plugins.sbt
addSbtPlugin("dev.cheleb" % "sbt-plantuml" % <version>)
In build.sbt
enablePlugins(PlantUMLPlugin)
*.puml file under src/main/resources/diagram/ will be processed and *.png file outputed to target/scala-X.XX/resource_managed/main/diagram
plantUMLSource
plantUMLTarget