become -> ansible_become

For some of these, the `ansible_` prefix does not seem to be needed,
but it's the canonical way to do things and it may become required in
newer Ansible versions.

Related to #3237

examples/hosts

@@ -2,8 +2,8 @@
 # If you'd rather use a local IP here, make sure to set up `matrix_coturn_turn_external_ip_address`.
 #
 # To connect using a non-root user (and elevate to root with sudo later),
-# replace `ansible_ssh_user=root` with something like this: `ansible_ssh_user=username become=true become_user=root`.
-# If sudo requires a password, either add `become_password=PASSWORD_HERE` to the host line
+# replace `ansible_ssh_user=root` with something like this: `ansible_ssh_user=username ansible_become=true ansible_become_user=root`.
+# If sudo requires a password, either add `ansible_become_password=PASSWORD_HERE` to the host line
 # or tell Ansible to ask you for the password interactively by adding a `--ask-become-pass` (`-K`) flag to all `ansible-playbook` (or `just`) commands.
 #
 # For improved Ansible performance, SSH pipelining is enabled by default in `ansible.cfg`.