To add for instance a directory scripts to the distribution package:

1. Add to the project a folder scripts

2. On top of the build.sbt, add:

   import NativePackagerHelper._
   

3. In build.sbt, add a mapping to the new directory:

   mappings in Universal ++= directory("scripts") 
   

4. Build the distribution package with activator dist. The newly created archive in target/universal/ should contain the new directory.