Update the required rust version for build in readme

[cryptoni9n]

Currently, the readme states:

ord requires rustc version 1.67.0 or later. Run rustc --version to ensure you have this version.

When trying to build ord from source, the following message is received:

error: package `clap_builder v4.5.2` cannot be built because it requires rustc 1.74 or newer, while the currently active rustc version is 1.72.0
Either upgrade to rustc 1.74 or newer, or use
cargo update -p clap_builder@4.5.2 --precise ver
where `ver` is the latest version of `clap_builder` supporting rustc 1.72.0

running rustup update and updating to 1.77.0 bypasses this error.