Support installation with cargo-binstall

[codito]

Is it possible to allow installation with cargo-binstall?

This crate is available on crates.io from https://github.com/pepa65/offline-chess-puzzles fork. Also tagging @pepa65 for suggestion.

[pepa65]

Because of the rapid advances in Brian's repo, I have more or less retired my version (renamed it to OCP and recloned this repo under the proper name) and hope to contribute my improvements (Dutch translations, some cleanup of the config and where to save the db, some clearer messages, and a "standalone" binary) as time allows.

(My repo is now on github.com/pepa65/OCP and cargo-binstall should continue to work, but will not have all the improvements that offline-chess-puzzles has received lately.)

I do hope this repo can be published on crates.io, and make a binary available for cargo-binstall as well.