Added a small clarification to a snippet for order of execution

[ghost]

I added some clarifications because people coming over from Python or C++ often get flipped by the fact that a=a+b does not refer to the process of assignment but rather to an operation.

[vahidk]

I think this is too far in to describe these basics. I'll think of a way to add these clarifications to the first item.

[ghost]

Okay.