I've just spent a few minutes building the project and getting it to run, I thought I'd mention some tidbits:

1. The instance URL should not include a trailing /. Example invocation that worked for me: RUST_LOG=info ./target/release/tafkars-lemmy https://myinstance
2. Once running I was able to access the API using curl -v http://localhost:8000/top.json or curl -v http://localhost:8000/r/mycommunity/top.json