Add some docs for commands, scripts, available settings

docs/base/config/available/overview.rst

@@ -0,0 +1,18 @@
+
+Overview
+========
+
+All settings are (usually) optional, meaning the app will fall back to some
+default value if the setting is not found in config.  And you can put
+essentially whatever you like in your config file (or the DB ``setting``
+table), so in that sense "all settings are available".
+
+But what we want to do here is, define certain common ("available") settings
+which any given Poser/Rattail app can leverage if needed, because the logic to
+do so is part of the underlying framework.
+
+We will present each in terms of how they would be defined in a config file, as
+opposed to DB table.  Often you can store the setting in the DB if you prefer,
+but in some cases the setting *must* be stored within a config file, because
+the app logic will only read it from file, and ignore the DB value.  For more
+info see :doc:`../overview` and :doc:`../db`.