docs: use available encryption vars instead of configuration extension

Signed-off-by: gardar <gardar@users.noreply.github.com>

docs/configuring-playbook-mautrix-bridges.md

@@ -46,11 +46,8 @@ matrix_bridges_encryption_default: true
 **Alternatively**, for a specific bridge:
 
 ```yaml
-matrix_mautrix_SERVICENAME_configuration_extension_yaml: |
-  bridge:
-    encryption:
-      allow: true
-      default: true
+matrix_mautrix_SERVICENAME_bridge_encryption_enabled: true
+matrix_mautrix_SERVICENAME_bridge_encryption_default: true
 ```
 
 ## relay mode