Allow proguarded jar to be launched straightaway

With the right bash header

build.sbt

@@ -230,6 +230,17 @@ lazy val cli = project
     },
     packExcludeArtifactTypes += "pom",
     resourceGenerators in Compile += packageBin.in(bootstrap).in(Compile).map { jar =>
+      import java.nio.file.Files
+      import java.nio.charset.StandardCharsets
+
+      val content = Files.readAllBytes(jar.toPath)
+      val header =
+        """#!/usr/bin/env sh
+          |exec java $JAVA_OPTS -noverify -jar "$0" "$@"
+        """.stripMargin
+
+      Files.write(jar.toPath, header.getBytes(StandardCharsets.UTF_8) ++ content)
+
       Seq(jar)
     }.taskValue,
     ProguardKeys.proguardVersion in Proguard := "5.3",