feat(u/riking/aoc/day01): add day01 solution

Tests with the puzzle's sample inputs are included.

Change-Id: I32cd59b9e3894bde3d67ebdc3a977961b17bdb49
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2223
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Tested-by: BuildkiteCI

users/riking/adventofcode-2020/day01/default.nix

@@ -0,0 +1,10 @@
+{ depot, ... }:
+
+with depot.third_party;
+
+naersk.buildPackage {
+  src = ./.;
+
+  buildInputs = [];
+  doCheck = true;
+}