Update README to include creating one-time payment products

README.md

@@ -18,6 +18,8 @@
 ```
 
 ### Adding new products
+
+##### Recurring product (subscription)
 ```
 (ucloud-cli) [test@ungleich ucloud-cli]$ UCLOUD_PAY_SERVER=http://127.0.0.1:5000 python ucloud.py product add \
 --name xxxxxxxxxxxx \
@@ -32,6 +34,18 @@
 
 ```
 
+##### One-time payment product
+```
+(ucloud-cli) [test@ungleich ucloud-cli]$ UCLOUD_PAY_SERVER=https://ucloud-pay-dev.ungleich.ch python ucloud.py product add \
+--name xxxxxxxxxxxx \
+--realm xxxxxxxxxxxx \
+--seed xxxxxxxxxxxx \
+--product-name "One time membership" \
+--product-description="One time membership fees" \
+--product-type=one-time \
+--product-price=3500
+```
+
 ### Register a payment method (cc for now)
 
 ```