function addResourceFile(f) {
    return (f || [])
      .map(asset =>
        project.addResourceFile(
          path.relative(projectConfig.sourceDir, asset),
          { target: project.getFirstTarget().uuid }
        )
      )
      .filter(file => file)   // xcode returns false if file is already there
      .map(file => file.basename);
  }
This function works in a similar manner to its Android version,
except it does not copy fonts but creates Xcode Group references