More or less in order to have a show case and working example.
There is no huge benefit in that case.
But it demonstrates that a default.nix could call callPackage and
benefit from 1:1 copy of nixpkgs package definition.
Also eases debugging of the derivation / package.
Does not exist yet, add own derivation via overlay.
Exclude tests for documented reasons.
Fix broken indentation in readme.rst
(used as test case for installed rst2pdf);