Update examples/vars.yml: add a whitespace character for indenting

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

examples/vars.yml

@@ -12,7 +12,7 @@ matrix_domain: example.com
 # The Matrix homeserver software to install.
 # See:
 #  - `roles/custom/matrix-base/defaults/main.yml` for valid options
-# - the `docs/configuring-playbook-IMPLEMENTATION_NAME.md` documentation page, if one is available for your implementation choice
+#  - the `docs/configuring-playbook-IMPLEMENTATION_NAME.md` documentation page, if one is available for your implementation choice
 #
 # By default, we use Synapse, because it's the only full-featured Matrix server at the moment.
 #