This example needs stdlib MIR to do anything interesting.
Make sure you have cargo-seer installed:
cargo install seer --git https://github.com/dwrensha/seer
Then run seer in this directory, with:
RUSTFLAGS="-Z always-encode-mir" xargo seer
(It's weird that we need to set RUSTFLAGS like that, because cargo-seer should already handle it. Is this a bug in xargo?)