Rename file to prevent common mistake

Prompted by this: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/779#issuecomment-764807507

docs/configuring-playbook.md

@@ -10,7 +10,7 @@ You can then follow these steps inside the playbook directory:
 
 - create a directory to hold your configuration (`mkdir inventory/host_vars/matrix.<your-domain>`)
 
-- copy the sample configuration file (`cp examples/host-vars.yml inventory/host_vars/matrix.<your-domain>/vars.yml`)
+- copy the sample configuration file (`cp examples/vars.yml inventory/host_vars/matrix.<your-domain>/vars.yml`)
 
 - edit the configuration file (`inventory/host_vars/matrix.<your-domain>/vars.yml`) to your liking. You may also take a look at the various `roles/ROLE_NAME_HERE/defaults/main.yml` files and see if there's something you'd like to copy over and override in your `vars.yml` configuration file.