Add spec file for building in RPM-based systems.

With this file, in a RPM building environment you can use `rpmbuild -bb path/to/mu.spec` and obtain a set of RPM files (according to Fedora Packaging Guidelines) which can be installed on a system via `rpm`.

This specfile is working in a Fedora machine, other RPM distributions might have another name for some packages; but I'm not aware of them.