[IMP] update readme

sale_import_amazon/README.rst

@@ -9,7 +9,17 @@ Configuration
 
 To configure this module, you need to:
 
-#. Go to ...
+1. Create a Sale Channel called "Amazon"
+2. To avoid storing your credentials in database, you can define them in the configuration files of your "server_environment_files" module as following::
+
+	[sale_channel.Amazon]
+	lwa_appid = XXXX
+	sp_api_refresh_token = YYYY
+	lwa_client_secret = ZZZZ
+
+You can use the ``server_environment_data_encryption`` module if you want these configuration files to be encrypted.
+
+Check OCA's module `server_environment <https://github.com/OCA/server-env/tree/16.0/server_environment>`_ for more info.
 
 Usage
 =====