Polish up documentation
    
    - Use `Title Case` for headings
    - Consistently wrap `rpmautospec` in single backticks when referring to
      the project.
    - Consistently capitalize "Python", "Koji"
    - Improve phrasing in some places
    - Fix some warnings when building the documentation
    
    Signed-off-by: Nils Philippsen <nils@redhat.com>