Add narrative docs for app configuration

docs/narr/config/overview.rst

@@ -0,0 +1,36 @@
+
+Overview
+========
+
+The app uses a global :term:`config object` to keep track of its
+:term:`config settings<config setting>`.  See also :doc:`object`.
+
+The app must call :func:`~wuttjamaican.conf.make_config()` during
+startup to obtain the config object.
+
+Values come (mostly) from :term:`config files<config file>` and/or the
+:term:`settings table`.  See also :doc:`settings`.
+
+Values are always strings in their raw format, as returned by
+:meth:`~wuttjamaican.conf.WuttaConfig.get()`.  But the config object
+also has methods to coerce values to various types, e.g.:
+
+* :meth:`~wuttjamaican.conf.WuttaConfig.get_bool()`
+* :meth:`~wuttjamaican.conf.WuttaConfig.get_int()`
+* :meth:`~wuttjamaican.conf.WuttaConfig.get_list()`
+
+The config object is also responsible for creating the :term:`app
+handler`::
+
+   from wuttjamaican.conf import make_config
+
+   config = make_config()
+   app = config.get_app()
+
+   if config.get_bool('foo.bar'):
+       print('YES for foo.bar')
+   else:
+       print('NO for foo.bar')
+
+   with app.short_session() as session:
+       print(session.bind)