updated reamde

README.md

@@ -49,6 +49,9 @@ This are the properties you can configure and what are the default values:
 * `profile`: The AWS profile name for authentication. This ensures that the `~/.aws/credentials` AWS auth provider is used. By default this is empty and the default chain will be used.
     * **required**: false
     * **default value**: `""`    
+* `initial_position_in_stream`: The value for initialPositionInStream. Accepts "TRIM_HORIZON" or "LATEST".
+    * **required**: false
+    * **default value**: `"TRIM_HORIZON"`
 
 ## Authentication