Update configuring-playbook-bridge-mautrix-meta-messenger.md

Add " ' " around the username for matrix_admin.

docs/configuring-playbook-bridge-mautrix-meta-messenger.md

@@ -62,7 +62,7 @@ matrix_mautrix_meta_messenger_bridge_permissions_default:
   '{{ matrix_admin }}': admin
 ```
 
-If you don't define the `matrix_admin` in your configuration (e.g. `matrix_admin: @user:YOUR_DOMAIN`), then there's no admin by default.
+If you don't define the `matrix_admin` in your configuration (e.g. `matrix_admin: '@user:YOUR_DOMAIN'`), then there's no admin by default.
 
 You may redefine `matrix_mautrix_meta_messenger_bridge_permissions_default` any way you see fit, or add extra permissions using `matrix_mautrix_meta_messenger_bridge_permissions_custom` like this: