Restore perlrepository.pod in stub form

Give Perl doc sites a sane ‘latest’ version to display, directing readers
to current information, rather than showing the Perl 5.12 version in
perpetuity.

And help anybody typing man perlrepository find where the docs have moved
to.

Suggested by Father Chrysostomos in:
http://www.nntp.perl.org/group/perl.perl5.porters/2013/09/msg207079.html