Rewrite section "Using External Programs" / move to introduction of opening files chapter
https://testing.docs.gimp.org/2.99/en/gimp-using-external-programs.html
Because it says that Linux distributions almost always come with Ghostscript, that the Windows installer includes it. (I have no idea about Mac OS though.)
And because it is not about "using external programs" as an end-user ("Oh my god, I so want to use external programs!"). The section is only about dealing with PDF and PS formats.