clarify the config path

added path to the correct vars.yaml in matrix-synapse

docs/configuring-playbook-shared-secret-auth.md

@@ -4,7 +4,7 @@ The playbook can install and configure [matrix-synapse-shared-secret-auth](https
 
 See that project's documentation to learn what it does and why it might be useful to you.
 
-If you decide that you'd like to let this playbook install it for you, you need some configuration like this:
+If you decide that you'd like to let this playbook install it for you, you need some configuration ( matrix-docker-ansible-deploy/roles/matrix-synapse/vars/main.yml ) like this:
 
 ```yaml
 matrix_synapse_ext_password_provider_shared_secret_auth_enabled: true