Add ensure-matrix-users-created tag

Now that the Draupnir user may be auto-created in certain configurations (if a password is assigned), it's useful to have the tag there.

docs/configuring-playbook-bot-draupnir.md

@@ -147,7 +147,7 @@ After configuring the playbook, run it with [playbook tags](playbook-tags.md) as
 
 <!-- NOTE: let this conservative command run (instead of install-all) to make it clear that failure of the command means something is clearly broken. -->
 ```sh
-ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,start
+ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,ensure-matrix-users-created,start
 ```
 
 **Notes**: