Add submission for Day 1

[hipstermojo]

This submission includes both challenges for day 1

[mattgathu]

Awesome. Do you mind refactoring your PR to match what I did here: https://github.com/rust-nairobi/aoc-2020/pull/1/files

That way your submission remains in its own file and multiple people can contribute without touching main.rs

[mattgathu]

I will add a short guide on the README on how to do the pull requests :-)

[hipstermojo]

I still haven't seen the guide on the README. Also, maybe we can all use the cargo-aoc crate for more uniformity?

[mattgathu]

Sorry, I dropped the ball.

I've added the section on how to contribute.