Successfully sent a message from my local #SofaPub server to myself at infosec.exchange. The command I used was:
cat ./hello_world.json | sofapub post https://infosec.exchange/inbox
The JSON file is just an ActivityPub Create message I created by hand in Emacs.
Also uploaded sofapub to crates.io. You can install it with `cargo install sofapub` and run the executable right away. I'll update the documentation shortly to align with that usage.