readme: use simpler mysql GRANT query
readme: use simpler mysql GRANT query

adiferd/docker-gitlab-ci,bboehmke/docker-gitlab-ci,outcoldman/docker-gitlab-ci,youhong316/docker-gitlab-ci,outcoldman/docker-gitlab-ci,sameersbn/docker-gitlab-ci,youhong316/docker-gitlab-ci,sameersbn/docker-gitlab-ci,adiferd/docker-gitlab-ci,bboehmke/docker-gitlab-ci