[Metafacture] More maintainers for Metafacture

[Christoph Böhme]

Hi all,

I just want to let you know that Pascal Christoph and Fabian Steeg have
become maintainers for the metafacture-core repository and the
metafacture organisation on Github. As they are very active users and
contributors, I think this will help to support development of
Metafacture in the future. Especially, as I changed jobs and will not
work with library data in the future any more.

Best,
Christoph