message: add help text to cache commands
diff: @@ -48,9 +48,11 @@ struct Run {
  #[derive(Debug, StructOpt)]
  enum Cache {
  + /// Clear the cache
  #[structopt(name = "clean")]
  Clean,
  + /// Display the location of the cache
  #[structopt(name = "dir")]
  Dir,
  }
  