[Basics] Update about.md (#3733)

Corrected sum in example on line 155.

Author: BethanyG

concepts/basics/about.md

@@ -152,7 +152,7 @@ def add_two_numbers(number_one, number_two):
 # the variable will also return the value.
 >>> sum_with_return = add_two_numbers(5, 6)
 >>> print(sum_with_return)
-7
+11
 ```
 
 Functions that do not have an _explicit_ `return` expression will _implicitly_ return the [`None`][none] object.