Clarify why comparing things to none is discouraged

[gandhis1]

This page: http://docs.quantifiedcode.com/python-anti-patterns/readability/comparison_to_none.html

Is a little tautological, i.e. "it is preferred". I think it could elaborate more on why the == operator it is not preferred.

This could be used as a reference:

https://stackoverflow.com/questions/3257919/what-is-the-difference-between-is-none-and-none

[adewes]

Cool! Do you want to make a PR with this suggested edit?