docs: update sudo_session_timeout in README

closes #34

README.md

@@ -245,7 +245,7 @@ By default, a password will be said to have been recently seen if it has been
 seen in the last 10 minutes. You can change this configuration if needed:
 
 ```ruby
-Authie.config.sudo_timeout = 30.minutes
+Authie.config.sudo_session_timeout = 30.minutes
 ```
 
 ### Working with two factor authentication