docs: add some narrative docs to explain basic concepts

still needs a lot of work i'm sure..gotta start somewhere

docs/narr/cli/builtin.rst

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+
+===================
+ Built-in Commands
+===================
+
+Below are the :term:`subcommands <subcommand>` which come with
+WuttaSync.
+
+It is fairly simple to add more; see :doc:`custom`.
+
+
+.. _wutta-import-csv:
+
+``wutta import-csv``
+--------------------
+
+Import data from CSV file(s) to the Wutta :term:`app database`.
+
+This *should* be able to automatically target any table mapped in the
+:term:`app model`.  The only caveat is that it is "dumb" and does not
+have any special field handling.  This means the column headers in the
+CSV file must be named the same as in the target table, and some data
+types may not behave as expected etc.
+
+Defined in: :mod:`wuttasync.cli.import_csv`
+
+.. program-output:: wutta import-csv --help

docs/narr/cli/custom.rst

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+
+=================
+ Custom Commands
+=================
+
+This section describes how to add a custom :term:`subcommand` which
+wraps a particular :term:`import handler`.
+
+See also :doc:`wuttjamaican:narr/cli/custom` for more information
+on the general concepts etc.
+
+
+Basic Import/Export
+-------------------
+
+Here we'll assume you have a typical "Poser" app based on Wutta
+Framework, and the "Foo → Poser" (``FromFooToPoser`` handler) import
+logic is defined in the ``poser.importing.foo`` module.
+
+We'll also assume you already have a ``poser`` top-level
+:term:`command` (in ``poser.cli``), and our task now is to add the
+``poser import-foo`` subcommand to wrap the import handler.
+
+And finally we'll assume this is just a "typical" import handler and
+we do not need any custom CLI params exposed.
+
+Here is the code and we'll explain below::
+
+   from poser.cli import poser_typer
+   from wuttasync.cli import import_command, ImportCommandHandler
+
+   @poser_typer.command()
+   @import_command
+   def import_foo(ctx, **kwargs):
+       """
+       Import data from Foo API to Poser DB
+       """
+       config = ctx.parent.wutta_config
+       handler = ImportCommandHandler(
+           config, import_handler='poser.importing.foo:FromFooToPoser')
+       handler.run(ctx.params)
+
+Hopefully it's straightforward but to be clear:
+
+* subcommand is really just a function, **with desired name**
+* wrap with ``@poser_typer.command()`` to register as subcomand
+* wrap with ``@import_command`` to get typical CLI params
+* call ``ImportCommandHandler.run()`` with import handler spec
+
+So really - in addition to
+:func:`~wuttasync.cli.base.import_command()` - the
+:class:`~wuttasync.cli.base.ImportCommandHandler` is doing the heavy
+lifting for all import/export subcommands, it just needs to know which
+:term:`import handler` to use.
+
+.. note::
+
+   If your new subcommand is defined in a different module than is the
+   top-level command (e.g. as in example above) then you may need to
+   "eagerly" import the subcommand module.  (Otherwise auto-discovery
+   may not find it.)
+
+   This is usually done from within the top-level command's module,
+   since it is always imported early due to the entry point.

docs/narr/cli/index.rst

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+
+========================
+ Command Line Interface
+========================
+
+The primary way of using the import/export framework day to day is via
+the command line.
+
+WuttJamaican defines the ``wutta`` :term:`command` and WuttaSync comes
+with some extra :term:`subcommands <subcommand>` for importing to /
+exporting from the Wutta :term:`app database`.
+
+It is fairly simple to add a dedicated subcommand for any
+:term:`import handler`; see below.
+
+And for more general info about CLI see
+:doc:`wuttjamaican:narr/cli/index`.
+
+.. toctree::
+   :maxdepth: 2
+
+   builtin
+   custom