package-groups: Add "Brainstorming" page from Fedora Wiki for packages
    
    This commit imports the old "i3/Brainstorming" wiki page and converts it
    to AsciiDoc. While the wiki page was more broad, this time I narrowed
    the scope to focus specifically on the package groups.
    
    My hope is by adding this to the docs, we can review changes to the
    package groups through Pull Requests and issue discussions.
    
    https://fedoraproject.org/wiki/SIGs/i3/Brainstorm
    
    Signed-off-by: Justin W. Flory (he/him) <git@jwf.io>