This example was adapted from Xubai Wong's [`simpleAdd`](https://github.com/xubaiw/lean-lake-build-script-demo/tree/758373277cb8615f9b9cb43025fa7d59d6b0badb/simpleAdd) Lake demo.
Done with [permission](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/leanpkg.2B.2B.20idea.20.5BRFC.5D/near/246711345) from the author.