Document gitlab:db:decomposition:connection_status rake task

doc/settings/database.md

@@ -675,10 +675,20 @@ this.
 ### Configuring multiple database connections
+> The `gitlab:db:decomposition:connection_status` Rake task was [introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/111927) in GitLab 15.11.
+
 In GitLab 16.0, GitLab will default to using two database connections, that point to the same
 PostgreSQL database.
-If you want to opt-in for this feature, you can update this setting in `/etc/gitlab/gitlab.rb`:
+To opt-in for this feature, you first need to ensure PostgreSQL `max_connections` is high enough (using more than 50% of the available max connections).
+You can verify this by running the following Rake task:
+
+```shell
+sudo gitlab-rake gitlab:db:decomposition:connection_status
+```
+
+If the task indicates that `max_connections` is high enough, you can enable this feature by updating
+this setting in `/etc/gitlab/gitlab.rb`:
 ```ruby
 gitlab_rails['databases']['ci']['enable'] = true