Add some more "handler" docs

app handler, batch handlers, native batch types, people handler

docs/data/batch/native/importer.rst

@@ -0,0 +1,19 @@
+
+Importer Batch
+==============
+
+**Batch Type Key:** ``importer``
+
+**Purpose:** Allows user to preview an importer run before committing it.
+
+**Default Handler:** :class:`~rattail:rattail.batch.importer.ImporterBatchHandler`
+
+Normally when an importer runs, e.g. via command line, it reads data
+from the host system and writes it to the local / target side.  If in
+dry run mode, then the local data is not actually written.  But it's
+normally "all or nothing" in the sense that you either want to commit
+all the writes, or else you don't (dry run).
+
+It's also possible to write the import data to a batch, which can then
+be previewed and perhaps even adjusted.  Then executing the batch will
+"finalize" the import using data from the batch.