Documentation convention for marking unstable APIs.

[simonw]

I'm going to document this but mark it as unstable, using a new documentation convention for marking unstable APIs.

Originally posted by @simonw in #1154 (comment)

[simonw]

Can use an "admonition" similar to this:

.. warning::
    Restricting access to tables and views in this way will NOT prevent users from querying them using arbitrary SQL queries, `like this <https://latest.datasette.io/fixtures?sql=select+*+from+facetable>`__ for example.

As seen on https://docs.datasette.io/en/stable/authentication.html#controlling-access-to-specific-tables-and-views

Documentation: https://docutils.sourceforge.io/docs/ref/rst/directives.html#specific-admonitions

[simonw]

I'm going to use the existing .. warning:: pattern for this.