It didn't mention `matrix_appservice_discord_client_id` and `matrix_appservice_discord_bot_token`, which makes it hard for beginners. Related to #105 (Github Pull Request).
Prerequisites
Configuring your DNS server
Configuring this Ansible playbook
Installing
Registering users
Configuring service discovery via .well-known
Maintenance / checking if services work
Maintenance / upgrading services
Maintenance / PostgreSQL
Maintenance and Troubleshooting
Uninstalling