fix: Clarification and mistake in the docs

Author: n0nSmoker

README.md

@@ -430,7 +430,7 @@ There are two ways to do it:
 ```python
 import pytz
 
-item.to_dict(timezone=pytz.timezone('Europe/Moscow'))
+item.to_dict(tzinfo=pytz.timezone('Europe/Madrid'))
 ```
 - But if you do not want to write this code in every function, you should define
   timezone logic in your custom mixin (how to use customized mixin see [Custom formats](#Custom-formats))

sqlalchemy_serializer/serializer.py

@@ -288,7 +288,7 @@ def serialize(self, value, key=_UNSPECIFIED):
 
         Args:
             value: The value to be serialized.
-            key: The key to be serialized.
+            key: The key associated with the value (for nested structures).
 
         Returns:
             The serialized value.