- document installing other parts of the USC SIPI database

  problem: it is not recommended to install after installation is complete as
  this will not modify the packlist (for uninstalling later)

- sequences, e.g.,

      use Sort::Naturally;
      nsort grep {  $_->basename =~ /^6\.1\./  } @{ Data::TestImage::DB::USC::SIPI->get_installed_images() }