basic_auth should be required for writer API

[piyusql]

Although the read api can serve without authentication by default.
But strongly we should use authentication for any updates in our database.

https://github.com/vmware/bridgeql/blob/cb3055ac88f352d2531d1e0cd4036e96a4e0d805/bridgeql/django/settings.py#L16

we can use bridgeql.django.auth.basic_auth as default writer option.
Please update README accordingly.