Tell the user they can skip ahead if they need to

At the end of the `Ensure GitLab is running` step, the user should have
a working setup and may be done with the guided tour.  It may be the
user has a problem, so instead needs to jump ahead to troubleshooting,
but the current structure is:

* Required information
* Initial node configuration
  * Consul
  * Database
  * Pgbouncer
  * Application
* Node post configuration
  * Consul
  * Database
  * Pgbouncer
  * Application
* Failover
* Restore
* Alternative configuration
* Troubleshooting

Here we just add a link to the end of 'Node post configuration / Application', rather than restructure.

doc/administration/high_availability/database.md

@@ -537,7 +537,7 @@ gitlab-rake gitlab:db:configure
 #### Ensure GitLab is running
 
 At this point, your GitLab instance should be up and running. Verify you are
-able to login, and create issues and merge requests.
+able to login, and create issues and merge requests.  If you have troubles check the [Troubleshooting section](#troubleshooting).
 
 ### Failover procedure