Add specific PSQL instructions for clarity

doc/administration/external_database.md

@@ -13,5 +13,24 @@ If you use a cloud-managed service, or provide your own PostgreSQL instance:
    [database requirements document](../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.
-   This step is covered in [Configuring GitLab for HA](high_availability/gitlab.md).
+1. Configure the GitLab application servers with the appropriate connection details
+   for your external PostgreSQL service in your `/etc/gitlab/gitlab.rb` file:
+
+    ```ruby
+    # Disable the bundled Omnibus provided PostgreSQL
+    postgresql['enable'] = false
+
+    # PostgreSQL connection details
+    gitlab_rails['db_adapter'] = 'postgresql'
+    gitlab_rails['db_encoding'] = 'unicode'
+    gitlab_rails['db_host'] = '10.1.0.5' # IP/hostname of database server
+    gitlab_rails['db_password'] = 'DB password'
+    ```
+
+    For more information on GitLab HA setups, refer to [configuring GitLab for HA](high_availability/gitlab.md).
+
+1. Reconfigure for the changes to take effect:
+
+   ```shell
+   sudo gitlab-ctl reconfigure
+   ```