Added migration guide to README

Author: sergioteula

README.md

@@ -8,7 +8,8 @@ A simple Python wrapper for the [last version of the Amazon Product Advertising
 [![Support](https://img.shields.io/badge/Support-Good-brightgreen)](https://github.com/sergioteula/python-amazon-paapi/issues)
 [![Amazon API](https://img.shields.io/badge/Amazon%20API-5.0-%23FD9B15)](https://webservices.amazon.com/paapi5/documentation/)
 
-> If you are still using the old version, go [here](https://github.com/sergioteula/python-amazon-paapi/blob/master/amazon/README.md) for documentation.
+> If you are still using the old version, go [here](https://github.com/sergioteula/python-amazon-paapi/blob/master/amazon/README.md) for documentation or check our
+[migration guide](https://github.com/sergioteula/python-amazon-paapi/docs/pages/migration-guide.md).
 
 ## Features