Expanded the authoring instructions.
    
    The guidelines authoring instructions have been amended to:
    · Recommend Asciidoctor as a lightweight way of previewing one's changes.
    · Point out that there is a command-line program in rubygem-asciidoctor.
    · Explain how the purpose of the container-based method differs from the purpose of the Asciidoctor method.
    · Mention that the makefile will download container blobs.