Add custom file to iOS resources directory

I need to include some custom files (sound files) in the resources directory of iOS build.
I’ve tried something like this in the main config.xml file:

  <platform name="ios">
    <resource-file src="resources/sound.wav" />

But on command ionic build iOS the file is not copied on the resources directory of the iOS build.
Is there a way to obtain this?

I think this is only for plugins

I’m with the same problem, but with Android. I use the tag to copy a mp3 file into res/raw folder and nothing is copied. Anyone already had this problem before?