chore(docs): update README.MD with information about fraction digits (#…

…494)

* chore(template): update readme.md with info about the currency convertions

* chore(readme.md): add reference to the payments sdk

* chore(readme.md): update readme.md

README.md

@@ -31,6 +31,16 @@ The template contains two modules :
 
 Regarding the development of processor module, please refer to the following documentations:
 
+### Currencies
+
+A special note regarding the usage of currencies and working with them. commercetools provides monetary values in cent amounts which adheres to the <https://en.wikipedia.org/wiki/ISO_4217> standard.
+
+This means that for the currency `EUR` the minor units will be expressed with fraction digits of 2. I.e. a value of 1 euro and 50 cents will be expressed as `150`. Some currencies have 0 or even 4 fraction digits.
+
+It's important to note that individual PSP could differ from this standard and/or require special attention when passing data between the connector and psp. So it's important to convert properly on the input and output layer when interacting with PSP.
+
+commercetools provides the library [connect-payments-sdk](https://github.com/commercetools/connect-payments-sdk) which includes various utility function to help with these conversions.
+
 - [Development of Processor](./processor/README.md)
 
 #### 1. Develop your specific needs