Document `CI_SHARED_ENVIRONMENT` and `CI_DISPOSABLE_ENVIRONMENT`
Document `CI_SHARED_ENVIRONMENT` and `CI_DISPOSABLE_ENVIRONMENT`

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