Update pgbouncer documentation

Add a first pass at notes about how to connect a standalone instance of
pbgouncer into GitLab

doc/administration/high_availability/pgbouncer.md

@@ -17,6 +17,49 @@ See our [HA documentation for PostgreSQL](database.md) for information on runnin
 
 ### Running Pgbouncer as part of a non-HA GitLab installation
 
+1. Generate PGBOUNCER_USER_PASSWORD_HASH with the command `gitlab-ctl pg-password-md5 pgbouncer`
+
+1. Generate SQL_USER_PASSWORD_HASH with the command `gitlab-ctl pg-password-md5 gitlab. We'll also need to enter the plaintext SQL_USER_PASSWORD later
+
+1. On your database node, ensure the following is set in your `/etc/gitlab/gitlab.rb`
+   ```ruby
+   postgresql['pgbouncer_user_password'] = 'PGBOUNCER_USER_PASSWORD_HASH'
+   postgresql['sql_user_password'] = 'SQL_USER_PASSWORD_HASH'
+   postgresql['listen_address'] = 'XX.XX.XX.Y' # Where XX.XX.XX.Y is the ip address on the node postgresql should listen on
+   postgresql['md5_auth_cidr_addresses'] = %w(AA.AA.AA.B/32) # Where AA.AA.AA.B is the IP address of the pgbouncer node
+   ```
+
+1. Run `gitlab-ctl reconfigure`
+
+1. On the node you are running pgbouncer on, make sure the following is set in `/etc/gitlab/gitlab.rb`
+
+   ```ruby
+   pgbouncer['enable'] = true
+   pgbouncer['user'] = {
+     'pgbouncer': {
+       'password': 'PGBOUNCER_USER_PASSWORD_HASH'
+     }
+   }
+   pgbouncer['databases'] = {
+     gitlabhq_production: {
+       host: 'DATABASE_HOST'
+     }
+   }
+   ```
+
+1. Run `gitlab-ctl reconfigure`
+
+1. On the node running unicorn, make sure the following is seti in `/etc/gitlab/gitlab.rb`
+
+   ```ruby
+   gitlab_rails['db_host'] = 'PGBOUNCER_HOST'
+   gitlab_rails['db_password'] = 'SQL_USER_PASSWORD'
+   ```
+
+1. Run `gitlab-ctl reconfigure`
+
+1. At this point, your instance should connect to the database through pgbouncer. If you are having issues, see the [Troubleshooting]() section
+
 ### Interacting with pgbouncer
 
 ## Troubleshooting