Mention matrix_common_after_systemd_service_start_wait_for_timeout_seconds in failure message

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1062

roles/matrix-common-after/tasks/start.yml

@@ -44,6 +44,9 @@
         {{ item }} was not detected to be running.
         It's possible that there's a configuration problem or another service on your server interferes with it (uses the same ports, etc.).
         Try running `systemctl status {{ item }}` and `journalctl -fu {{ item }}` on the server to investigate.
+        If you're on a slow or overloaded server, it may be that services take a longer time to start and that this error is a false-positive.
+        You can consider raising the value of the `matrix_common_after_systemd_service_start_wait_for_timeout_seconds` variable.
+        See `roles/matrix-common-after/defaults/main.yml` for more details about that.
     with_items: "{{ matrix_systemd_services_list }}"
     when:
       - "item.endswith('.service') and (ansible_facts.services[item]|default(none) is none or ansible_facts.services[item].state != 'running')"