Add initial/basic docs for batches

that still needs a lot yet i'm sure, but is a start

docs/data/batch/schema.rst

@@ -3,4 +3,26 @@
 Batch Table Schema
 ==================
 
-TODO
+From a schema standpoint there are 2 types of batches generally speaking:
+static and dynamic.
+
+Static batch types have 2 "dedicated" tables within the ``default`` schema of
+the DB: one table for the batch "headers" and another for its "data".  For
+instance the basic inventory batch uses these tables:
+
+* ``batch_inventory``
+* ``batch_inventory_row``
+
+When a new inventory batch is created, 1 new ``batch_inventory`` record is
+created but multiple new ``batch_inventory_row`` records may be created.  The
+latter table contains all rows for all inventory batches.
+
+Dynamic batch types however are just that, and do not have a dedicated "data"
+table, although they still do have a dedicated "header" table.  For instance
+this approach is used for "importer batches" - when running an importer creates
+a batch, it will create 1 new ``batch_importer`` record but then will create a
+brand new table with custom schema based on the importer, to hold the data.
+
+To avoid cluttering the ``default`` schema within the DB, dynamic batch data
+tables are not stored there.  Instead they are kept within the ``batch``
+schema, which must be manually created if you need it.