chore(tazjin/finito): Add build configuration

Adds a Naersk-based build to check that this compiles, with a Lockfile
based on the ~2018 crate versions.

Change-Id: I0460a476d3b983fcf71e35e6b480f4a526118b58
Reviewed-on: https://cl.tvl.fyi/c/depot/+/803
Reviewed-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/finito/default.nix

@@ -0,0 +1,5 @@
+{ depot, ... }:
+
+depot.third_party.naersk.buildPackage {
+  src = ./.;
+}