link to database requirements document in HA database docs

doc/administration/high_availability/database.md

@@ -13,6 +13,8 @@ Database Service (RDS) that runs PostgreSQL.
 
 If you use a cloud-managed service, or provide your own PostgreSQL:
 
+1. Setup PostgreSQL according to the 
+   [database requirements document](doc/install/requirements.md#database).
 1. Set up a `gitlab` username with a password of your choice. The `gitlab` user
    needs privileges to create the `gitlabhq_production` database.
 1. Configure the GitLab application servers with the appropriate details.