Announce some playbook changes

CHANGELOG.md

@@ -1,3 +1,24 @@
+# 2022-11-22
+
+# Automatic `matrix_architecture` determination
+
+From now on, the playbook automatically determines your server's architecture and sets the `matrix_architecture` variable accordingly.
+You no longer need to set this variable manually in your `vars.yml` file.
+
+# Docker and the Docker SDK for Python are now installed via external roles
+
+We're continuing our effort to make [the playbook use external roles for some things](#the-playbook-now-uses-external-roles-for-some-things), so as to avoid doing everything ourselves and to facilitate code re-use.
+
+Docker will now be installed on the server via the [geerlingguy.docker](https://github.com/geerlingguy/ansible-role-docker) Ansible role.
+If you'd like to manage the Docker installation yourself, you can disable the playbook's installation of Docker by setting `matrix_playbook_docker_installation_enabled: false`.
+
+The Docker SDK for Python (named `docker-python`, `python-docker`, etc. on the different platforms) is now also installed by another role ([com.devture.ansible.role.docker_sdk_for_python](https://github.com/devture/com.devture.ansible.role.docker_sdk_for_python)). To disable this role and install the necessary tools yourself, use `devture_docker_sdk_for_python_installation_enabled: false`.
+
+If you're hitting issues with Docker installation or Docker SDK for Python installation, consider reporting bugs or contributing to these other projects.
+
+These additional roles are downloaded into the playbook directory (to `roles/galaxy`) via an `ansible-galaxy ..` command. `make roles` is an easy shortcut for invoking the `ansible-galaxy` command to download these roles.
+
+
 # 2022-11-20
 
 ## (Backward Compatibility Break) Changing how reverse-proxying to Synapse works - now via a `matrix-synapse-reverse-proxy-companion` service