OK, I've clearly missed someting here.
I've got D8.05 running, and have subthemed Bootstrap.
I'm trying to turn on Twig debugging, to no avail. (I just want to move my h1.page-title).
I've copied default.services.yml to services.yml in my sites/default; I've set debug: true and auto_reload: true in sites/default/services.yml.
I've also created settings.local.php and uncommented the render cache and dynamic page cache there.
I created sites/default/development.services.yml by copying sites/development.services.yml.