install doc with python group

[db]

On 11 Jul 2017, at 14:44, Joshua Root <jmr at macports.org> wrote:
> Only the subports like py27-setuptools_hg and py35-setuptools_hg are supposed to install any files. py-setuptools_hg is a stub port, and as such has no distfiles and thus no extracted sources.

I know why it fails. The stub port does install the subport as a dependency though (first one of python.versions, I guess, which is not clear-cut in the guide). I suppose I could change ${worksrcpath} — how would you make the subport install the documentation when installing the stub port?