Improve onboarding in readme

[schriftgestalt]

As someone unfamiliar with rust and fontc, I would need some help getting started. Are there and how to get precompiled binaries? How to do a local debug build?

[anthrotype]

no precompiled binaries yet. I'd start with installing the rust toolchain (https://www.rust-lang.org/learn/get-started) and then run cargo build (for default debug build) or cargo build --release, then you'll find the binaries in either target/debug or target/release sub-directories. cargo run -p fontc -- [fontc options] will rebuild and run fontc at the same time.

[schriftgestalt]

Can you put that into the readme?

[rsheeter]

Pardon the delay, was out for TPAC. Does #455 help?

[rsheeter]

Closing, please reopen if it's still hard to get started.