Start datasette.json, re-add --config, rm settings.json

The first step in defining the new `datasette.json/yaml` configuration mechanism.

Refs #2093, #2143, #493

docs/cli-reference.rst

@@ -112,8 +112,7 @@ Once started you can access it at ``http://localhost:8001``
       --static MOUNT:DIRECTORY        Serve static files from this directory at
                                       /MOUNT/...
       --memory                        Make /_memory database available
-      --config CONFIG                 Deprecated: set config option using
-                                      configname:value. Use --setting instead.
+      --config FILENAME               Path to JSON/YAML Datasette configuration file
       --setting SETTING...            Setting, see
                                       docs.datasette.io/en/stable/settings.html
       --secret TEXT                   Secret used for signing secure values, such as

docs/configuration.rst

@@ -0,0 +1,10 @@
+.. _configuration:
+
+Configuration
+========
+
+Datasette offers many way to configure your Datasette instances: server settings, plugin configuration, authentication, and more.
+
+To facilitate this, You can provide a `datasette.yaml` configuration file to datasette with the ``--config``/ ``-c`` flag:
+
+    datasette mydatabase.db --config datasette.yaml

docs/settings.rst

@@ -47,9 +47,9 @@ Datasette will detect the files in that directory and automatically configure it
 The files that can be included in this directory are as follows. All are optional.
 
 * ``*.db`` (or ``*.sqlite3`` or ``*.sqlite``) - SQLite database files that will be served by Datasette
+* ``datasette.json`` - :ref:`configuration` for the Datasette instance
 * ``metadata.json`` - :ref:`metadata` for those databases - ``metadata.yaml`` or ``metadata.yml`` can be used as well
 * ``inspect-data.json`` - the result of running ``datasette inspect *.db --inspect-file=inspect-data.json`` from the configuration directory - any database files listed here will be treated as immutable, so they should not be changed while Datasette is running
-* ``settings.json`` - settings that would normally be passed using ``--setting`` - here they should be stored as a JSON object of key/value pairs
 * ``templates/`` - a directory containing :ref:`customization_custom_templates`
 * ``plugins/`` - a directory containing plugins, see :ref:`writing_plugins_one_off`
 * ``static/`` - a directory containing static files - these will be served from ``/static/filename.txt``, see :ref:`customization_static_files`