Whither "External Projects"?

I'm pretty well convinced that the new docs chapter "External Projects"
does not belong under the Client Interfaces volume. If it only covered
client interfaces then maybe it'd belong there, but it doesn't --- and
I'm sure that the discussion of non-interface projects will expand.

Another possibility is to put it in the Administrator's Guide, but that
seems to suffer from the opposite problem.

We could make it an Appendix, but that sort of amounts to burying the
info, which isn't what we want either.

I'm about half tempted to add it to the Preface.

Thoughts?

regards, tom lane