added a readme

README.md

@@ -0,0 +1,9 @@
+### Usage
+update the following in `invoice_data.json`
+* *invoice_due_date*
+* *reminder_start* (seconds before due date)
+* and *reminder_every* (reminder interval in seconds)
+for each customer_id
+
+### Running
+`$ python invoice.py` outputs the invoices and waits for the scheduler for reminder and invoice to complete.