Update typing-final.md

Author: williln

python/typing-final.md

@@ -4,6 +4,8 @@
 
 - [Python docs: `typing.final`](https://docs.python.org/3/library/typing.html#typing.final)
 
+## Notes 
+
 Adding the `@final` decorator to a class or class method indicates that the object cannot be overridden. You can't subclass that class and you can't override that method in a subclass. 
 
 You can add it to either a class or a method on a class.