chore: Add info about changing PO status when creating new PO line it…

…em (#97)

docs/create_purchase_order_line_item.md

@@ -4,6 +4,9 @@ Caution should be taken when creating a new line item in a purchase order. Each
 purchase order line item must have a line number and it must be unique among the
 other line items. It should be a non negative value.
 
+Note: This action will change purchase order `status` from `closed` to `open`, 
+if the purchase order is `closed`.
+
 After creating the new purchase order line item, you **must** update the the
 purchase order's `amount` field. This should be done once you are finished
 manipulating all of the line items.