Exercise 2: Add solution that uses built-in method

[nikitarevenco]

I feel like learners at this stage are likely to use a for loop so they may find it interesting to know that there is a built-in way of doing it. Of course just using it as the solution would defeat the point of the exercise so I've added it as a second solution

Maybe it could make sense to make this the solution, and the original solution will become commented out.