Icons and desktop integration

I finally managed to build my app using flatpak-builder. But i have no idea about how to put my icon and desktop files inside flatpak. the documentation says it should be put on /app/share/applications etc. But how do i do it:

  1. should i put the desktop files in my main repo and flatpak-builder automatically integrates them?
  2. should i put my desktop files and icons in flathub repo?
  3. should i just copy/paste them in to build-dir generated by flatpak-builder
  4. should i use post-install keyword in my yml file then copy my desktop file and icons into proper places. (if yes then why didn’t some flatpak manifests (yml files) do that?).