add repository info to Build.PL

Hi, I've added the URL for this repo to dist's metadata, so that it could show up nicely on [MetaCPAN](https://metacpan.org/pod/Config::Neat).

This PR is part of my [advent quest](https://questhub.io/realm/perl/quest/547b4202070ccf750d00010e).

Cheers,
Sergey.