To have launchd start redis at login:
    ln -sfv /usr/local/opt/redis/*.plist ~/Library/LaunchAgents
    
Then to load redis now:
    launchctl load ~/Library/LaunchAgents/homebrew.mxcl.redis.plist
    
Or, if you don't want/need launchctl, you can just run:
    redis-server /usr/local/etc/redis.conf