[docs] Add Fedora Badges design resources / how to design a badge
    
    This commit brings in the design resources recommended by the Fedora
    Badges designers, à la @riecatnor's style guide (circa 2014):
    
    https://riecatnor.wordpress.com/2014/02/24/fedora-badges-official-style-guide/
    
    This commit also closes this issue, since new documentation is available
    to explain how to create a Fedora Badge:
    
    https://pagure.io/fedora-badges/issue/528