Adding the square-root exercise about julia

[cmcaine]

Great! Good luck :)

The description of the task in problem-specifications is kinda bad, IMO. Here's my suggestion for what to use:

Find the square roots of positive non-zero integers.

You may want to check out the Wikipedia pages on [square roots][square-root] and [methods of computing square roots][computing-square-roots].

[square-root]: https://en.wikipedia.org/wiki/Square_root
[computing-square-roots]: https://en.wikipedia.org/wiki/Methods_of_computing_square_roots

Feel free to innovate on that!