Add doc about autocompleters

docs/data/autocomplete.rst

@@ -0,0 +1,25 @@
+
+Autocomplete
+============
+
+Even though autocomplete is generally most useful in a web app, e.g.
+for customer lookup, here it is implemented in the data layer and has
+no "web" parts to it per se.  (Which means you could add autocomplete
+to your console app?)
+
+An "autocompleter" in Rattail is really just an object with one
+important method,
+:meth:`~rattail:rattail.autocomplete.base.Autocompleter.autocomplete()`.
+
+Rattail comes with several autocompleters built-in.  You can get a new
+autocompleter easily enough from the app handler, and using it is just
+as easy::
+
+  products_ac = app.get_autocompleter('products')
+  results = products_ac.autocomplete('root beer')
+
+The results will be a list of dicts, each will have at least ``value``
+(uuid) and ``label`` (name/description) items.
+
+See also :class:`~rattail:rattail.autocomplete.base.Autocompleter` and
+:meth:`~rattail:rattail.app.AppHandler.get_autocompleter()`.

docs/data/index.rst

@@ -14,6 +14,7 @@ Data Layer
    sync
    versioning
    batch/index
+   autocomplete
    custorders/index
    reports/index
    problems