Demote cache-busting to secondary heading

docs/usage.rst

@@ -45,7 +45,7 @@ Then when you run ``collectstatic`` command, your CSS and your javascripts will
     $ python manage.py collectstatic
 
 Cache-busting
-=============
+-------------
 
 Pipeline 1.2+ no longer provides its own cache-busting URL support (using e.g. the ``PIPELINE_VERSIONING`` setting) but uses
 Django's built-in staticfiles support for this. To set up cache-busting in conjunction with ``collectstatic`` as above, use ::