clean up redirect from join.fp.o to docs/join
    
    previously the redirect from join.fedoraproject.org pointed to the old
    join page on the wiki, which in turn re-directed to the final (correct)
    destination of https://docs.fedoraproject.org/en-US/project/join/
    
    This commit sets the redirect from join.fp.o to the docs site, skipping
    the wiki altogether.
    
    Resolves: https://pagure.io/fedora-infrastructure/issue/10363
    
    Signed-off-by: Ryan Lerch <rlerch@redhat.com>