New module: AsciiDoc for Fedora Documentation Writers (part of #8)
    
    This is a first attempt at giving Fedora Documentation Writers a one-
    stop location to get started writing AsciiDoc. Instead of trying to
    rewrite existing documentation about AsciiDoc, I linked out to helpful
    resources maintained by the `asciidoctor.org` upstream.
    
    However, this commit does write new documentation about handy snippets
    to reuse in a Fedora-specific context. I also wrote a short guide on how
    to use reusable attributes, since I realize this is something I have
    done in many repositories I set up but never documented.
    
    Part of #8 to improve the new contributor experience to Fedora
    Documentation with AsciiDoc and Antora.
    
    Signed-off-by: Justin W. Flory <git@jwf.io>