[virt-manager]: restore usage examples
    
    originally, the libre.patch simply deleted the documentation usage examples;
      because they referred to non-FSDG-fit distros;
      and the 'osinfo-db' package has no definitions for FSDG-fit distros
    this commit adds back the usage examples, referring to FSDG distros instead
    the exact usage examples given will not work, without also adding
      the 'parabola' definition to the osinfo database
    the documentation is complete however; so that is already an improvement
    we could fork the 'osinfo-db' package, to add the parabola definition;
      but experimentation suggests that it can be accomplished
      via the 'libosinfo' package, which parabola already patches
    ideally, we should request that parabola be added to the osinfo-db upstream
      (which is probably a good idea anyways)