Document how to use DB_INITIALIZE and DB_MIGRATE
Document how to use DB_INITIALIZE and DB_MIGRATE

* Limitation of DB_INITIALIZE (run once)
* helm hooks
* Examples

axilleas/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,mmkassem/gitlabhq,iiet/iiet-git,dreampet/gitlab,stoplightio/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,axilleas/gitlabhq,iiet/iiet-git,iiet/iiet-git,mmkassem/gitlabhq,axilleas/gitlabhq,dreampet/gitlab