Add more docs for Feature Layer

not complete, but progress..

docs/features/custorders/fulfilment/index.rst

@@ -0,0 +1,20 @@
+
+Fulfilment
+==========
+
+In the context of Customer Orders, "fulfilment" requires that:
+
+* customer has paid for the product
+* customer has possession of the product
+* order data reflects these facts
+
+Some places will require the Customer to pay for the Order when they
+place it, in which case the first is taken care of already.  But if
+not, then the physical product can be rang up at POS when they come to
+pick up.
+
+If the product is paid for upon pick-up then Rattail has a way to
+"automatically detect" that fulfilment has occurred (by monitoring the
+POS Transactions).  But if payment happens up-front then likely some
+User must explicitly indicate to Rattail that fulfilment is complete,
+i.e. product was picked up by Customer.