how_to_handle_statics.rst: Update make command
how_to_handle_statics.rst: Update make command

`make css` has been renamed to `make assets`.

solarissmoke/django-oscar,django-oscar/django-oscar,django-oscar/django-oscar,django-oscar/django-oscar,solarissmoke/django-oscar,solarissmoke/django-oscar,django-oscar/django-oscar,solarissmoke/django-oscar