$ mkdir patches

$ quilt new test.diff
> Patch %{P}test.diff is now on top

$ echo foo > foo
$ quilt add foo
> File foo added to patch %{P}test.diff

$ quilt add patches/bar
> File patches/bar is located below patches/

$ quilt add %{QUILT_PC}/baz
> File %{QUILT_PC}/baz is located below %{QUILT_PC}/
