docs: Initial commit on how to join Badges community
    
    This commit creates a new page in our docs site about how to get
    involved and join the Fedora Badges community. It includes some basic
    instructions like how to register a FAS account, sign up to the mailing
    list, join the IRC/Telegram, etc.
    
    Once published, the page will be available here:
    
        https://docs.fedoraproject.org/en-US/badges/join/
    
    Signed-off-by: Justin W. Flory <git@jwf.io>